Put on raincoats and go splash in puddles! Love the water!
Put on swimsuits and go build sand castles in the rain!
Pretend to be ducks and seagulls! Hunt for worms like robins.
I would skip "Tag" on the grass (too slick), but most other games (freeze tag!) etc. can be played. Marco Polo - little running! Blow bubbles with dish soap if not raining too hard.
Put water based paint into spray bottles, and play in the rain! It will wash off quicker if your clothes are already wet!!
Put on laundry-ready dirty vacation clothes, then play in the rain! Add a bar of soap (bio-degradeable!) and "wash" each other!!
When my kids were younger, I held their shoes aside to keep dry, then let them get their clothes wet in sprinklers etc. With Crocs, that is not a problem. If lots of rain forcast, invest in Crocs!
Finger painting!! With water-based paint.
Hunt for rocks, make collections.
After the games, then popcorn, fireplace, hot chocolate, movies & blankets, etc. NAPS!!
have fun!!
C. W