Help with England Itinerary

York is one of my favorite places in Britain. We stayed at the Minster Hotel, located walking distance from the north gate. The dining is good there and they have parking for an auto.
Also, loved Durham for a day.
The Yorkshire Moors is very scenic, we drover through that on our way to Whitby.

We spent 2 weeks driving around South England from Salisbury to Canterbury in September 2022, so my recommendation would definitely include Sussex. Here's my Trip Report if you're interested.

https://community.ricksteves.com/travel-forum/trip-reports/trip-report-the-south-of-england

Look at www.nationaltrust.org.uk for some great photos and sites open to view by region. Check out what is included in their yearly membership for families or an Explorer Passes for specified length of time. It also includes country hikes, etc. We really enjoyed places that were not that crowded because they were a little off the main tourist trail. We also visited some of the English Treasure Houses which features totally furnished Estate Mansions like Chatsworth. British Heritage is another great site; they may have Passes. I'm sure others will be able give more info. The choises you gave is like picking the cutest kitten! Bon Voyage.

There are many other places to stay in Yorkshire than York and Grassington.

You could stay in Wensleydale or Swaledale- both of which are authentic James Herriot locations- where he actually worked, as opposed to just where the current TV adaptation is filmed. Swaledale in particular has a lot of mining history to it. But Wensleydale also has the likes of Bolton Castle, Middleham Castle and Jervaulx Abbey for instance, plus the town of Richmond (including it's Castle and authentic Georgian theatre).

How exciting! What are your kids' interests?

What time of year are you planning on coming?

Will you be hiring a car?

How many days are you planning for London and how many does that leave you to play with? Are you p[anning on stopping in just one place and doing day trips from there, or move around a bit more?

What are the kids wanting to see/do?

Yorkshire - either the Dales of North York Moors would work well as would Dorset.

Alternatively there is East Anglia - Norfolk and Suffolk - which is an area ignored by many tourists but would tick all the boxes.

These are all lovely places to visit and I'm sure you'll enjoy any of them. My pick would be Yorkshire as there's so much to do up there- from the south bordering the Peak District to the north and the Dales, and the beautiful coastline. I would even recommend venturing further north into Durham/Northumbria (noting that Durham is in county Durham, not Yorkshire). Most of the major sites in Surrey and Sussex can be done easily as day trips from London if you prefer less moving around.

I have to add my vote for Yorkshire. It is gorgeous. My daughter and I did an All Creatures Great and Small tour that included Grassington, and it was great.

Thanks for all the great replies. To answer specific questions:

My 10 yo daughter is probably most interested in sites she'll recognize from books/movies (I got her into Austen and Christie early, she loves Dr. Who, All Creatures, etc). My son is football focused, but that will not be the focus of this trip ;) I think he'll also appreciate WWII history as he's studying that in school.

What time of year are you planning on coming? August 2026

Will you be hiring a car? Likely once we leave London, though I love a good train trip.

How many days are you planning for London and how many does that leave you to play with? Are you p[anning on stopping in just one place and doing day trips from there, or move around a bit more? 2-3 nights in London. 4-5 nights elsewhere. We would definitely stop places on the way or do day trips as necessary.

If your son is wanting to cover WW2 sites, then do consider a tip to Bletchley Park, home of the WW2 codebreakers.

From York, do try and visit Eden Camp on the outskirts of malton. This was a prisoner of war camp and the huts now form a museum covering the social and military history of World War II and subsequent modern conflicts. Ther are alos military vehicles and airplanes around the site.

Both have a lot to see and it isn't just 'war stuff' and there will be plenty to interest your daughtr too.

The Imperial War Museum in London is interactive; which is fun to experience. It is built on the site of the old Bethleham Hospital which became to be known as "Bedlam", There is a Imperial War Museum pass which includes other sites such as the ship HMS Belfast which is moored on the Thames and the Royal Air Force Museum at Duxford located near Cambridge.

I guess we've been to York 3x (well, last time just to rent a car). In 2001, we travelled with our 3 kids (17, 14, and 11). Our kids loved York. We had Britrail passes so went by train from London.
In addition, we have driven to York from Heathrow, and we also have trained to York and rented a car there for Yorkshire (stayed in Northallenton as well as Grassington). We rented from Arnold Clark in York, as well as 2x from Heathrow. Don't forget the real "James Herriot" (Alf Wight) home/museum in Thirsk, near York.

There is so much to do in London, too!