Quite possibly some of the best rainy day or indoor activities we've come across on Pinterest from Inner Child Fun. I once painted the windows of our classroom with the children and they looked fab (just make sure you add ova glue and washing up liquid before painting. - 10 Rainy Day Activities for Kids
Someone else said: I think this is one of the best toddler activity idea websites I've ever found. The ideas are simple, educational and allow for creative exploration of the child's own world. Highly recommend.
Pinner says "This kept my 2 year busy for an entire hour and my 4 year old busy for 2 hours! Drop vinegar tinted with food coloring onto a pan filled with baking soda. Sheer minutes of colorful fizzy fun!"