Kids outdoor play areas? (Tokyo)

Hi,

We are new in Tokyo (Meguro) with 3 kids aged 14, 11 and 7. They have more energy than can be contained in a house so need a park or outdoor area where they can throw or kick a ball and run off some energy. We've visited several parks but been confronted with ornamental trees and signs to stay off the grass and no ball games.

Can anyone recommend anywhere similar to what we traditionally call parks where kids can play ball games? Even a public basketball hoop would be good.

Thanks!

Karl