There is the aquarium close by if you want to spend more money!
Or cross over the river, go up to Trafalgar Square, then either walk down to Buckingham Palace, or walk down to the Houses of Parliament via Whitehall , see Downing Street and the Horseguards on parade. Or walk up to Leicester Square and visit China Town, or cross over at Leicester Square tube and go to Covent Garden.
(ps as you walk up Villiers street to the strand to get to Trafalgar square there is a very good gelato shop on the right hand side)
Or walk over to Embankment Pier and catch a river boat down to Greenwich , lots of things to see on the way HMS Belfast, Tower of London, Tower Bridge, Canary Wharf etc etc and Greenwich has lots to see and do, Observatory, Maritime Museum etc.
While you are near the London Eye walk down to the Festival Hall, there are loads of kid friendly chain eateries there, like Giraffe, Prezzo, other pasta and pizza places , or if you are feeling adventurous there is a foodie market behind the festival hall that has great pop up stalls. Festival Hall handy for toilets too, or if it is a rainy day and you have your own food there are places in there to sit and eat it ( discreetly!)
Have a great day.