Ideas of fun things for 5 & 7 yo boys to do in London?

[oilandwater]

I'm desperate for some new ideas of things to do in London with my 5 & 7 yo boys, especially with half-term looming. Any ideas? Bonus points for physical activities and or crafty things -- willing to pay reasonable amount of ££ to keep them occupied and me sane.

(and if someone can suggest a more appropriate topic for me to post this on, please do!!)

Where in London are you? Can suggest some holiday activities in south london but that might not be terribly helpful!

Science museum fabulous fun! Imperial war museum, London Transport museum, Greenwich park and Observatory, The Diana Memorial park In Kensington Gardens, London Dungeons, Ripley's in Piccadilly Circus, Welcome trust museum on Euston Road, The South Bank has loads of fun activities and Somerset House - have a look on their website to see what activities they have on - usually free.
Have fun!

There's a children's festival on at the South Bank- I just booked a few things for half term for my boys but there are free activities too. Both Tates have kids arty activities. Mine have enjoyed all the boats: HMS Belfast, the Cutty Sark, The Golden Hinde.

Go all round the DLR at the front of the train pretending to drive. Stop off for dim sum at the Regatta Centre by Prince Regent. Cross the river by cable car then get them to get you to the Maritime Museum in Greenwich, and/or the Observatory up a steep hill in Greenwich Park.
Crystal Palace Park has the life size model dinosaurs, a city farm with reptile room, and excellent cafe.

Don't go to the NHM dinosaurs during half term - tried by mistake last one and it was 30 min queues just to enter the building, 2 hours for dinos. The investigation centre in the basement was a.hit though.

London Aquarium and park nearby (pretty much under London Eye).

Camley Street Natural Park (near King's Cross)

Definitely second the free museums.

Think your boys would be into Geocaching?

I second the DLR trip to Greenwich. At Island Gardens there is a foot tunnel under the Thames to Greenwich (free) and has stairs up/down to tire them out a bit.

Playground at Greenwich Park, stand in two time zones at the top of the hill straddling the meridian line.

Chislehurst Caves - go underground. Good if its cold/wet.

All of above plus Tower of London. Hampstead Heath.

Free museums can be nightmarishly busy in half term though. I'd plan an early start!

Horniman museum has a programme of kids events. It also has a park, a small aquarium and a GIANT stuffed walrus. What on earth could be better than that, eh? Have fun!