To ask for engineering-based activities in Londonfor 9/10yo

[Squarestones]

Hello, due to delegation mess up I need to sort some activities for DS and cousin (9 and 10) next week in London. I thought they were booked into a workshop at the RI but they are not....so looking for something fun, ideally a bit educational, science or engineering themed, to send them to for a day or half day to complement other more physical and screen-based activities across the week. Thanks in advance for any ideas 🙂
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Bumping up for any London mumsnetters or indeed just Stem experts

WonderLab at the Science Museum is the obvious one.
Tower Bridge tour? (You get to go in the room where they keep the lifting equipment).
HMS Victory?
Museum of London may have something suitable (the Smithfields' branch - Museum of London Docklands has a terrific hard hat section but it's for younger kids).
Do you mean something you can leave them at unsupervised though?

Thanks @Needlenardlenoo yes Wonderlab is currently top of the list - I will investigate your other suggestions, I think tower bridge might interest them.
Not worried about staying with them on a tour/activity, more just trying to get something which will engage them a bit more than a standard visit, as their elder siblings are doing quite a cool workshop on that day and don't want moaning about who had the more interesting day

They are 9 & 10 - just include a trip to a great ice cream place or equivalent and let them pick something the size of their heads. It will then be the best day ever and outshine whatever carefully curated activity you plan.

That said HMS Belfast and Imperial War museum were popular with mine when younger.

😂oh there will be plenty of treats @RaisedVegBeds - we are in charge of them all for a week so I just need a few bits which are more structured/cultured to balance out the cinema trips, swimming, video games, park, water fights in garden, etc etc which will also be on the agenda.

I was popping on here to suggest the RI! But Brunel's Tunnel Rotherhithe or Tower Bridge - you see the working mechanisms for opening the bridge.

Tower Bridge is cool.

Brentford Steam and Water Museum is good - but it is in Brentford
https://waterandsteam.org.uk/

Bazelgette’s Sewer System walking tour and Thames Tideway tour? And/or Crossness pumping station. Don’t think Crossness is open everyday though so may not match up with your days. But in any case a great example of Victorian engineering and a bit of modern engineering.

Tower Bridge, Thames Barrier exhibition (small I think) or London Transport Museum?

Maritime museum in Greenwich?

Crossness is fabulous but it's in Bexley which is probably not what the OP means by "London".

Imperial War Museum was always popular with mine (and its free) - they have a range of activities over the summer holidays https://www.iwm.org.uk/events/family-activities-iwm-london

The main hall is pretty cool with planes hanging from the ceiling etc. Its also in a park so they can have a run around and you could have a picnic - Co op store between the Museum and Waterloo to pick stuff up.

Afterwards you could take a trip on the Uber boats (cheaper than the tours)