Fun and easy, only a little bit messy...
Cover a cookie sheet with a thin layer of baking soda. Put vinegar and food colouring in squeeze bottles or use a medicine dropper and cup. Have the kids drop the vinegar on the baking soda - it will bubble up.
The kids really love it!
Doesn't have to be just for valentine's day, but I made the vinegar red this week to make it go it's the theme.
