The Ultimate Guide to Hands On Toddler Activities - Brittany Estes--- This could also work for pre-math skills. Which shape has more or less? I would put on magnets on the back and have a magnetic work space for them to do this activity!
Colorful Fizzy Fun: 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!