Free or not £££ things to do near Hyde Park with young kids

[Rollerbird]

Got a 7 and 4 yr old coming to see Frozen. We will have a full other day to do stuff. Staying near Hyde Park just past Marble Arch.
Planning science museum, Buckingham palace (just to look) any other ideas?

The Diana Memorial Playground is in the northeast corner of Kensington Gardens, which is the east side of Hyde Park. It's an adventure playground based on Peter Pan and would suit your children's ages. It's free and adults are not allowed in without a child.

Thank you!

Natural History Museum seems the other obvious one

Which side of Marble Arch? There's Green Park and St James Park with the fountains and pelicans, easy walk to Buckingham Palace. Drop into Fortnums children's department.

Go on a paddle boat on the serpentine?

Kids can also paddle in the Diana fountain (south side if Serpentine) if it's not too cold.

Just off edgeware road near Argos. Need also something to do whilst wielding a big rucksack for 3 hours before the train on departure day!! (From Euston)

There's a left luggage office at Euston which costs £7.50 for 3 hours. It would.be worth it but make sure you leave enough time to retrieve your rucksack.