Perfect For a Wet Weekend

I recently went to the Museum of Childhood near Bethnal Green, which as the name suggests exhibits toys, dolls and games that date back to the 16th century. It was a really enjoyable visit and satisfied many of the criteria I look for in a museum
1. its free
2. its not too big and can be done in an hour or two
3. kids don't get bored too quickly
4. interesting building / space
5. nice coffee

Next on my list is the Museum of Brands, which looks interesting. If anyone's been, do let me know.