London: Need help with 4 day Itinerary with Autistic 7 year old/one parent

I am traveling to London in a few weeks (late July/early August) for one week, but we technically have only 4 days to sight see with two other adult friends. My son is a child with mild Autism and I will be taking his special needs buggy.

Would you mind helping me with my itinerary? Not yet in itinerary: We want to see Peter Pan @ Kensington Park/Gardens and we also have to squeeze in a dinner with friends wherever we can meet. We also want the double decker bus experience and the River cruise experience somehow -- How do we do that, where to fit in?
And the Harry Potter experience -- visiting 9 3/4 platform.Notting Hill visit, too.

My draft of the itinerary is below:

Thanks!

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London Itinerary:

Arrive: Wed, 29 July: Rest Day

Thursday 30th July: Kensington & South Kensington
Ease into that Thursday with some easy stuff: Princess Diana Memorial Playground in nearby Kensington Gdns, Play date with friends children. Picnic Lunch with kids.
-- Natural Museum of History: There is a Butterfly Garden inside, a new exhibit that has hundreds of living butterflies flying about the place, where you can touch them, walk with them, etc. Free museum, butterly: 6 quid.

FRI: St. James/Westminster
--Big Ben (just for the picture and to hear its bell)
* Westminster Abbey (but the last admission is 3:30) - across from Big Ben apparently
* London Eye (You don't have to suffer! We'll go--it's only 30 min.)
*Dali Museum
*Dinner with mates somewhere local

SAT: The City
--Tower of London
-- is it possible to have a Boat ride past London Bridge to Tate Modern?
--Tate Modern
--Trafalgar Square & Cafe in the Crypt (it's inside St Martin in the Fields at Trafalgar Sqare! A crypt!!)

SUN:
--Play date and lunch in North London
--Perhaps visit the Kings Cross station? (Platform 9 3/4)
--Piccaddilly Circus
--Trafalgar Square et al (if we had not seen it yet)

MON:
--Check out flat, taxi to Paddington, train to Wales

I don't know how long certain visits take, and there are so many places to visit.