England travel with 2 kids (4yo and 6yo)

You don’t say where in Northumberland you’ll be traveling from, but the obvious tourist spot between there and London is York - beautiful city, lots to see and station near the centre. BUT, in my view most of the things of interest are for children older than 6 and I think an energetic 4 year old would struggle. Also, you would be there during school summer holidays and it would probably be very busy.

I suppose you could aim for the coast (Scarborough??) and she could play on the beach (the sea won’t be warm even in July) but that would be out of your way from the north to London.

York is an easy train stop. Walking the York City Wall is super fun for everyone. The Minster's windows are awesome! They have some famous antique streets. You could take a day trip from here to one of the beach villages, by bus.

It's more than halfway but I agree that York is probably a logical stop as you won't have to travel to get somewhere from the station.

Where in Northumberland are you going? I love that area and I think your kids will love it as well. Hopefully you will have some time to do some sightseeing up there as there are many beautiful and scenic places to visit.

Northumberland and the North East of England generally is one of the cheaper parts of the country and there’s loads to see and do so it would be a good place to spend most of your trip and then combine it with a few days in London. There are glamping options but be aware the weather in that part of the world can be fairly cool even in July. Whereabouts in Northumberland is the wedding?

Thanks for the input thus far! The wedding is in Newton-by-the-Sea and there seem to be many options for places to stay. Seems to be a lot to explore in that area, and we will definitely plan some seaside time!

The easy way to do the car hire for Northumberland is to go by train to Newcastle and there is a car rental depot actually at the station- turn left out of the entrance and it is maybe a hundred yards away on your left. It's Enterprise.
Several places to stay actually in Newton Village.
You are only just up the road from Dunstanburgh Castle and the lovely fishing village of Craster- do get some smoked fish (especially kippers) from one of the smokeries at Craster.
And not far in the other direction to Seahouses for boat trips to the Farne Islands and Lindisfarne (Holy Island)- if the tides are against you driving to the latter.
Although maybe not what it is best known for there are wonderful beaches and sand dunes on Lindisfarne.
Embleton Bay (at Dunstanburgh) is one of Northumberland's great beaches and usually blissfully quiet.
Longhoughton Beach (on the drive down to Alnmouth and Alnwick) is another great and usually empty beach- a low tide beach, and one which is great for rockpooling.

Northumberland is wonderful for children and there's so much space to run round and work off energy. Newton-by-the-Sea is a good base to spend a few days to explore. isn31c has already suggested several. The walk from Craster above the beach to the ruined Dunstanburgh Castle is one of the best local walks - it is very easy and safe for the kids.

York would be my immediate thought of a suitable place to stop. The Museum Gardens in the centre of York is a large open area with plenty of space to run and explore (go and find the Multangular tower...) They might also enjoy Jorvik and a trip back into York's Viking past (complete with smells and sounds...)
https://www.jorvikvikingcentre.co.uk/
DIG ties in nicely with this as they can go and dig up things and learn about being an archaeologist.
https://www.digyork.co.uk/

There is also the National Railway museum too - Entry is free (donation appreciated) and it something different, if not just thge size of the locos...

For car rentals, there are a number of rental agencies near the Newcastle train station, including Europcar, Enterprise, National and a few others. My personal favorite is Arnold Clark, which has a location in Newcastle but it's about a 13 minute drive away. However, many of the AC branches will offer you a pick up and drop off at the train stations so it's definitely worth asking (they did that with me earlier this year when I returned my car in Carlisle). I've used Arnold Clark on my last two trips to the UK. Earlier this year I rented directly with AC (17 day rental) and then in 2023, I rented from them through their broker, Celtic Legend (14 day rental) for my trip to Scotland. Both rental experiences went very well. Arnold Clark is a pleasure to deal with. Their agents explain everything to you and make sure that you understand the fine print. They are good about upgrading sometimes (my last trip I was upgraded to a Mercedes at no extra cost), and very courteous and helpful. I will always use them in the UK for future rentals.

EDIT: I agree with wasleys about the walk to Dunstanburgh Castle. It has some great sea views and there is the fun of visiting castle ruins at the end. To get there, the easiest way is to park at the Craster Tourist Information Centre (there is a large car park there). From there, just walk past The Jolly Fisherman, past the harbour and towards the castle.

Try to visit Holy Island (Lindisfarne), which is wonderful, but check the tide tables before you go! I think kids would love it as there are lots of places to run around and a lovely beach they can play on and toss stones. I saw a lot of kids playing there when I was there earlier this year. Bamburgh Castle is another fascinating castle to visit.

My grandsons also like the ruined Warkworth Castle. If the Hermitage is open (included in ticket cost) it is worth the short walk to get the boat across the river to see it.

Enterprise, National and Alamo are all in the same office at Newcastle Central Station- not surprising as they are all Enterprise brands.

Europcar is the other side of the railway tracks- turn right out of the station then right at the Lit and Phil, through a long tunnel under the tracks (a narrow road) then right at the far side.
The Lit and Phil (Literary and Philosophical Society) is worth looking into for a free tour if there is one on at the right time. They also do a lot of talks, and lunchtime jazz or classical concerts. But it's best known for it's reference library.
And less than 5 minutes walk down the same street from the Lit and Phil is Newcastle Anglican Cathedral (St Nicholas')- free entrance.

It is probably closer to 25 minutes drive into Central Station from Arnold Clark at Birtley at the moment- traffic is diverting to any road it can due to an emergency (probably permanent) closure of a major road viaduct at Gateshead.
It is believed the viaduct will have to be demolished and rebuilt due to poor quality concrete.
If I was being thoughtful while that is happening I would ask AC to meet me at Chester-le-Street railway station (hourly direct train from York)- closer and easier for them.
Then heading for Northumberland from CLS avoid Newcastle entirely and take the A1 past the Metro Centre then over the Blaydon Bridge, straight into Northumberland. From the north side of the Blaydon Bridge it's the same avoiding route as you take coming across from Cumbria/Hexham etc. That is a good fast road.

Fly into Newcastle airport, rest at a hotel, then rent a car at the airport and head up to Newton by the Sea.

Keep the car until you return to Newcastle, then take the train straight to York or London. It's three hours from Newcastle to London so it is not long really

Fly home from London so you need to look for a multi-city flight: into Newcastle, return from London.