Isle of Wight?

There’s a pretty good bus service on the island, it doesn’t go everywhere however. Lots to do. Shanklin is gorgeous (Google image it!) Ventnor (at the bottom of the island) is a classic seaside town in a microclimate.
Lots of dinosaur history in the area, a nice little zoo and a garlic farm!

There are the model village in Godshill and the Isle of Wight Steam Railway that he might like. He also might like the chair lift to the beach at Needles.

Memory Seekers on YouTube has a playlist on the Isle of Wight that has been very useful in my planning for an upcoming trip to the Isle in September.

I just returned from multiple nights in Portsmouth with a day trip to Isle of Wight. Train from London is easy (unless a tree falls on the track and then a signal problem in Wimbledon disrupts the line. Don't ask.....)

I can't comment on all the things a 10 year old might like on Isle of Wight - I visited Osborne House only and returned to Portsmouth. There was one bus per hour between the ferry at Ryde and Osborne House. Many stops, so slow. I didn't check other bus routes to the other side of the island as I didn't have time to explore. But, I would advise looking at public transit schedules before deciding a car isn't necessary. I took a taxi one direction to Osborne House, 20 minute ride. The island is bigger than I had anticipated before I began my research.

The ferry to Isle of Wight is very convenient as is the hovercraft. Your grandson would probably enjoy either. Victoria and Albert's children spent many summers at Osborne House. In addition to the house, which might be more appealing to adults than kids (depends on kid obviously), the children's playhouse, gardens and toy fort can be explored. Lots of walks around the property including down to the beach.

As regards Portsmouth, that could easily be longer than a one day visit. There are many attractions at the Historic Dockyard. Opening times and ferry rides between the two sides of the harbor make it all but impossible to see all the ships and exhibits in one day. I think many 10 year olds would love exploring the various ships, weapons museum, submarine, harbor cruise, etc. For example, free rein to climb around and explore a Victorian war ship - the Warrior - as well as other ships to explore.

I know RS says Portsmouth is do-able as a day trip from London, but in my opinion, he is simply wrong unless the traveler wants to limit their visit to one or two ships at most. The Dockyards deserves much more time. The full attraction ticket is valid for one year - my companion and I spent two full days without repeating visits to ships or exhibits. We then spent part of another day re-visiting our favorites.

There is also the D Day Story in Portsmouth and Southsea Castle about a 40 minute walk from the Historic Dockyards. Large landing craft that can be explored at the D Day museum. The Castle is open for exploration, no charge.

P.S. - The Isle of Wight Festival was on-going at the time I visited - the music continues!

Bus service on the Isle of Wight is better than one usually finds on an island. Although there are exceptions, the buses tend to fan out from Newport, so you may end up there a few times, transferring. Unfortunately, Newport isn't a particularly interesting town. Look for a big tub of bus-schedule brochures at the ferry departure point. For me, having that printed schedule was a security blanket.

In addition to the places highlighted by Ade1983, Ryde and Cowes are attractive. Those are the two key ports. There are so many ferry options to the IOW it gets confusing. For your purposes, departures from Plymouth seem most convenient. My hydrofoil ran from Plymouth-Southsea to Ryde. Since I was heading to Winchester after IOW, I departed the island via the West Cowes-Southampton hydrofoil.

^^^^^Simplying - it isn't as obvious on paper as in reality. Acraven is correct - confusing.

From Portsmouth:

Wightlink Ferry - passenger ferry leaves from a departure area in the back of/through the Portsmouth Harbour train station. Footsteps from the Historic Dockyards area. Clearly marked. Hovercraft is down the beach a bit from the train station, but easy to find. Both arrive in Ryde harbour, slightly different locations. Major bus stop is also located at Ryde harbor.

We opted for the passenger walk-on ferry from Portsmouth Harbour since it was close to our hotel.

One of the interesting things on the island are it's Chines- deep ravine like wooded valleys. Shanklin Chine (and maybe others) have nightly illuminations when everything is lit up. I'm sure both the child and the big children would enjoy those.
@acraven meant Portsmouth, not Plymouth as the mainland port.

In some ways if going to Osborne House Southampton is the more obvious port to use on Red Funnel ferries. Although further from London it is a faster train ride then a shuttle bus to the docks. Ferries to West Cowes (then the cross river Chain ferry) or East Cowes. Easy train service Portsmouth to Southampton.

And if heading for The Needles and Alum Bay the Lymington to Yarmouth ferry is best. Lymington is like Portsmouth, a straight transfer train to ship.
Trains from London- just over 90 minutes to Brockenhurst for a quick change onto the branch shuttle. The open top bus to the Needles should still be running.
If you arrive by ferry to Ryde there is also the main line railway to Shanklin, which uses refurbished London Underground trains. Step straight off the ship onto the train.

I would imagine your grandson would enjoy both Carisbrooke Castle and Yarmouth Castle, both excellent well preserved castles to explore.

For food my children very much enjoyed The Cow. It's located on a farm and they specialise in burgers made with their own produce plus there's a variety of activities and interaction with some of the farm animals https://tapnellfarm.com/

Carisbrooke Castle also has the donkeys! These were used to turn the wheel drawing up water from the bottom of the well. There are still daily demonstrations. These are very popular so make sure you join the queue early to get a good view! It's also a good castle to explore.

Hello travel friends. Thanks for the feedback!

I am thinking we will spend 2 or 3 nights in Portsmouth instead. The dockyards sound fun, interesting and likely more appealing to our grandson. Last summer, he loved the WWII submarine on display in Chicago. Are there any tall ships in the dockyards? We are sailors and Jack Aubrey fans. And yes, I will google the area/tours.

We will probably opt for a day trip over to IOW.

So, any insights for staying/getting around in Portsmouth?

Thanks again. Love this forum.

Joe

I'm not sure what a "tall ship" category includes. Google tells me a large, traditionally-rigged sailing vessel. To me, that would be more like the Cutty Sark - a clipper ship - in Greenwich. That is fun to visit when in London. Read current reviews, but a few years back, we clambered all over. Another fascinating London ship is the HMS Belfast in the Thames. Good audio explaining usage in WWII and earlier as well as Brit nautical traditions - rum allocation, etc.

Portsmouth Harbour options at the museum - Main entrance side: Victorian Warrior- climb all over and explore freely; Nelson's Victory - under renovation but accessible for walk throughs with a good audio guide, lots of canons!, story of Nelson's last victory at Trafalgar; the Tudor Mary Rose - incredible resurrection of a 1500s era vessel - exhibit is very good with lots of artifacts, views of the Mary Rose and some videos at beginning and end to help a 10 (or 60) year old process the exhibit; WWI Gallipoli HMS M.33 - video story and walkthrough at your own pace, fascinating camouflage paintwork; several museum style exhibit halls with nautical artifacts and ships. Using the ferry provided by the Dockyards to the opposite side of the harbour - fascinating Explosion museum of weaponry through the ages and submarine HMS Alliance and submarine museum. Also, harbour ferry tour available. There are British naval ships docked at Portsmouth along with French ferries coming and going, so interesting things to see.

I found the website for the Dockyards a bit confusing and overwhelming when I was planning. On the ground, it's more obvious, but I was not aware of the necessity to be tied to a ferry schedule until on sight. The walk between the submarine museum and Explosion museum (after a ferry ride from the main museum site) is about 30 minutes - so my plans to do both in one day quickly and efficiently was no good. The HMS M.33 also had shortened visitor hours that I didn't expect. Once at Portsmouth, it may be worth taking a few minutes to "map out" a personal agenda for your visits.

We stayed at the Premier Inn Portsmouth Dockyard. This was my first experience of a Premier Inn. I know it is a favorite chain with many on this board. It is less than half a block from the Dockyards entrance and walkable (maybe 3 blocks) from the train station and ferry to I of W). My hotel review - I can't really complain. Very clean, staff was very good. Breakfast was acceptable, but nothing I would return for. The beds were not particularly comfortable, but room was larger than I expected. I think I am not a PI fan, but this place did fit the bill nicely for back and forth to the museum and transport. Price was good.

Also walkable from the PI and Dockyards is a mall and restaurant area - Gunwharf Outlets. We had a couple meals there with a number of chain type options, Wagamama, etc. As non-drinkers, we weren't interested in the pubs near the PI, but they were popular. There is a restaurant at the PI, we used only for breakfast.

It is probably a 45 minute walk from the PI or Dockyards to Southsea Castle and the D Day museum. I was given bus directions - major bus station right outside the train station. As we walled to the bus station, I saw a taxi rank and grabbed one of those instead. Quick ride to that area. We strolled back along the waterfront.

I don't know your itinerary, but Portsmouth was our last stop before Heathrow and return home. We took a National Express bus from the Portsmouth bus station by the train station direct to LHR and our last hotel - the Hilton Garden Inn. Much easier than train back into central London.

Summarizing - getting around Portsmouth was a breeze if the main interest is the Dockyards and SouthSea area. Tap and go for buses, taxis if desired, walkable to IOW Wightlink ferry and train. If you wanted to try the Southsea hoverport with the grandson, this might be a taxi ride - or a longer walk.

The Hovercraft runs a shuttle bus from The Hard bus station (by the Railway Station) in connection with all flights.

^^^ Good info - I wish I had known that a week ago! Maybe would have done both Wightlink ferry and Southsea Hovercraft just for the experience.

My posts referred to "the major bus station by the train station". This is The Hard Station Stuart mentions above - I should have indicated that. There are references to "The Hard" that a traveler is likely to come across.

Right at Gunwharf Quays is the Holiday Inn Express at which I had a good stay - good staff, standard HIE atmosphere. If you do stay there, and I'd recommend it, pack an extension cord because all electric plug points are on one side of the room, not the side with the bed. Very minor issue though...