Shapes is a simple app that lets your kids go through 20 different flat and spherical shapes. Shapes is from Five Pumpkins which as several other childrens apps for Android phones. The main reason I like this one better than the others is that you can turn off the prompts and allow your child to guess the shape, instead of just telling them. Do this changing the options to Quiz Mode.
I would love to see an update with more shapes in the future, but this is perfect for young children.