Hyde Park?

about a 45 minute walk from here,

and where is "here"?

Since I don't know where here is it is difficult to advise you.

If you are going to the Cabinet War rooms they are nowhere near Hyde Park.

They are adjacent to St James's Park and that flows off Green Park.

Do the boys (or you) like exotic water birds or other birds?

On the lake in St James's park, visible from the bridge but also the banks and even from the fence surrounding the park down by the War Rooms, are pelicans and all sorts of other exotic birds which wander freely. You can get as close as the birds let you.

You can drink alcohol in the parks, certainly the adults in the party. The Royal Parks website gives a list of picnic rules

https://www.royalparks.org.uk/park-management/park-regulations-and-policies/picnics-in-the-royal-parks

If your son enjoys WWII stuff there is lots in the Imperial War Museum to see and it is a free museum, recently refurbished. It is a tube ride from Hyde Park so might be worth seeing on another day. Not too far from London Eye and South Bank for instance.

Sorry, I mean google maps showed a 45 minute walk from the Natural History museum to the Churchill War Rooms.

I think she's saying she'll be at the Natural History Museum and then wants to head over to the Churchill War Rooms.

The adjacent Science museum is wonderful, you can walk through, picnic and feed the ducks in Hyde, Green and St. James parks en route to the War Rooms. Have you considered the Horse Guards Museum? http://www.householdcavalrymuseum.co.uk

I would never consider walking from South Kensington to Westminster Bridge. I'd have hopped a bus before I got a quarter of the way. But that's me.

I would think that 45 minutes for that walk (especially when you will be walking around the museum for 3 or 4 hours to see much of the basic information, but leaving plenty of the detail unseen) is ambitious, and you may be tired for the museum.

I would expect that the source you used does not take into account all the stopping at intersections you will be making while you wait for the green man. Or avoiding the other people and bicycles on the paths.

David is right; your son would probably enjoy the museum he told you about in London. I believe he would also enjoy the larger one in Duxford. They are both the Imperial War Museum, just two different locations. Here's the website for all Imperial War Museum locations: http://www.iwm.org.uk/

The Imperial War Museum has another location at Duxford, which is just outside of London. They are Britain's largest aviation museum and have 200 aircraft, military vehicles, many WW2 aircraft, and one of the Concordes on display.
http://www.iwm.org.uk/visits/iwm-duxford
If you are looking for a good day trip during your visit, you may all enjoy this.

No reason to walk other than it just always seems easier to me! But that was in Rome - London's system I think is easier, and we will have a travel card, so we can definitely tube or bus!

I'll look into those other museums too! So much to see, so little time!!

Thanks!!
Kim

ooh thanks for the IWM tip! That looks awesome, he is going to love it!

Just another perspective---we love to walk. And some of our favorite London walks have been through Hyde Park, Green Park, and St. James Park, or vice versa.

The first time we were there with our two daughters, age 11 and 14, we stayed near Westminster Bridge. The girls wanted to see Harrod's first thing so for some reason we asked at the hotel desk for advice on how long it would take The immediate answer was, "0h, no, you can't walk there." but we did, and it was fun for all of us. Maybe 45 minutes total. On that trip we never used the tube at all, and taxis only to go long distances.

Since that trip we have used the " three parks " route whenever appropriate. The other walking route we love is along the Thames, on the south side.

London is a wonderful city for walking. Just be mindful of the direction of the traffic, and seek out pedestrian lanes where they exist. You see so much more this way, instead of rushing place to place on the tube. We have used the bus when we reached the limits of our endurance. But I much prefer to remain above ground.