Why buy expensive bath time toys, when you have all the ingredients you need at home.  This is a recipe for bathtub finger paints:

1/3 c clear, mild dish detergent

1 T cornstarch

Food coloring

Mix detergent and cornstarch together in small bowl until blended.  Pour mixture into several sections of a plastic ice cube tray.  Add 1-2 drops of food coloring to each section of tray and mix.  

Use this to paint pictures and play games in the tub.  You can also use it as finger paint.  Enjoy!