My DDs (the 2 and 4 year old) LOVE to play with bubbles from the sink when I am doing dishes. They clap them together, spread them all over the floor, make "beards" and "hair" with them. It's the greatest toy ever for them.
The other thing that they both love is to take a cup of water and a paintbrush and "paint" anything and everything in the house. It's all pretty harmless 'cause there's only a tiny bit of water in the cup, and they have lots of fun painting on the table, chairs, wall, etc.