Squares, triangles, and circles. Playtime! When shapes start moving around, there's no telling what new shapes they can make--or how far they can go. Did you know that a bunch of triangles together can build a bigger triangle? Or that stacking a lot of little squares makes one giant one? And when circles start bouncing around, all sorts of things can happen--houses and castles spring up, magnificent fruit trees sprout, cars and trains hurry by, and . three, two, one . there's even a blastoff to Mars!.