New things to do for weekend in London

[janji]

Going to London in a couple of weeks for my birthday with dh and dc (aged 7 & 9). Going to the Ritz in the early evening on Saturday but would love suggestions of something's new to do. Have done the museums, Harrods, Hamleys, Covent Garden, Madam Tussards, Buck Palace before and would like new suggestions. Lost my job last year and this is a surprise trip from dh, but need to keep an eye on budget. Would love to do the London eye and the aquarium if anyone knows of any good deals or discounts?
Other than that, any other suggestions would be so gratefully received!!!
Thanks
Xxx

lots on at southbank eg beano town www.southbankcentre.co.uk/whatson/festivals-series/festival-of-neighbourhood/beanotown

boat to greenwich from emabankment (get regular river bus it is not expensive )

cable car from north greenwich and back again

web lab at science museum sciencemuseum.org.uk/visitmuseum/galleries/weblab.aspx

Thank you Cestla, ds would love the Beano stuff!