Fun thing to do in London with 10 year old

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We live in London so have done all the museums and normal stuff but I, looking for something extra fun/quirky to do this coming Saturday.

Any suggestions much appreciated

a) check out threads in the London topic (OK, it's gone a bit quiet of late, as people have been flinging threads in other places, but there are still enough there to be a decent resource all together)

b) what time of day?

c) what sort of things do you like to do?

Fancy a medal - running event (with entry fee) at QE Park on Saturday morning. Or free Parkruns all over the place

Check sites like The Londonist for weekend events listings

Walking over the top of the O2. Not sure if there is an age requirement.

RIB boat tour on the Thames.

Ghost walk.

And of course it's Open House weekend, but apparently ticketed events are all sold out. But there are still plenty of places you can just turn up and queue for

openhouselondon.org.uk

Postal museum with Mail Rail
Cable car
Wetland centre

My ten year old really enjoyed the Thames Rocket experience.

London Street Art Tour - the two hour one was about the right length of time
If you're near Dulwich - the Colour Palace is still there but going very soon, and it's free!
We are going to Poo Bergers at Aldgate Square - says it is family fun to celebrate Joseph Bazalgette's 200th Anniversary - and again it's free

Brick Wonders at the Horniman Museum www.horniman.ac.uk/visit/exhibitions/brick-wonders#image-0 They also have a crazy golf course which we enjoyed.