We went to our local playground today (we live in NYC and don’t have a backyard) and I saw something genius.
A blow up pool! A mom bought it to the park, blew it up and let all the kids play! I’ll be picking one up this week. She told me she buys a new one every year, but they aren’t very expensive anyway (maybe $5 or $10) and this way her 4 (!) kids stay near it.