Fine motor, colors, numbers, SO many learning activities these can be incorporated into. Stacking alone works fine motor, gross motor, hand-eye coordination, logic/reasoning skills...Count forwards and backwards. Line them up and add counters above or below or BOTH to work on one-to-one correspondence and rote counting. Turn them over and draw for a number to see if it is next in line. Color match with my full set color matching items or items in the environment. Or add them to a tinker tray and let the children come up with their own activities.