This ColourfulWobbly Stacker is a great one for encouraging hand-eye coordination. Children also learn to discriminate objects by size. Initially, the baby may simply remove the rings and need help to stack. You could then remove some rings and start by offering two rings to stack and then more upon mastery. It may take some time before they stack according to size. The wobbly base helps the child as it isn't knocked over so easily while they are in the early stages of learning how to stack.