This may be one of my favorite indoor activities for 18-24 month olds! (Although older and younger kids love it too. Just make sure to keep an eye on them!)
Amy was a little fussy one evening, so I put about an inch of water in a large Tupperware container on a towel on the kitchen floor, gave her some kitchen utensils (measuring spoons, straw, ladle) and let her play.
She loved it an was grumpy no more! She got a little wet, but water is okay with me!