6 months & up. The stackers include six graduated, numbered cups that are great to use for stacking, nesting, sorting and water play. Each cup is numbered from 1 to 6 on the bottom and is volumetrically accurate. The sorter is an elliptical shaped sorter with 8 colorful shapes to fit in corresponding holes. Each piece slides easily into the chute cut-outs on both the top and bottom of the sorter. Colors may vary.