What to do in SW London?

[tailsandscales]

I’m taking my 5 yo for a weekend in London in a couple of weeks.
On the Saturday morning we are going to Wimbledon but not planned what to do in the afternoon. Is there anything nearby that would be fun for a 5 yo, indoors (as probably will be cold and wet), not heaving with tourists and preferably close to tube so we don’t have to get a bus? Any suggestions?