There are extensive lists of things to do with children out there, but let me break it down for you, and especially my list is free entry!
Whether you are visiting or living in London, check those places guaranteed to please your little ones.

Top 5 Museums:
The Science Museum in South Kensington:
All floors are worth a visit and don’t forget to head to “The Garden” in the basement, an interactive space with construction, water, sounds and lights.
The Natural History Museum , right next door to the Science museum. Ideal for young fans of dinosaurs and full of wildlife collections.
The Transport Museum in Covent Garden. Obsessed with cars/buses/trains etc? Then this is the place to take them.
The Royal Air Force Museum London in Colindale, with the outdoor playground being a definite win.
The V&A Museum Of Childhood in Bethnal Green. Ok, this one is maybe more for the adults, as it is an exhibition of toys collected over the years, with some nostalgic items.

Top 5 Playgrounds:
Soooo many to choose from, a quick Google search will help you locate them.Those are my favorites:
Kensington Gardens Diana Memorial playground
Parliament Hill playground and paddling pool
Hyde Park playground
Highbury Fields playground
Holland Park Adventure playground

Top 5 City Farms:
Ok, they aren’t the London Zoo but a good free alternative and way less crowded. Head to:
Kentish Town City Farm
Freightliners Farm
Oasis Farm Waterloo
Vauxhall City Farm
Stepney City Farm
Enjoy those free places, it’s more money for icecreams!