Babies develop their hand-eye co-ordination at around six months. At this age, they are more mobile and begin to improve their fine motor skills. The coordination between both their hands also improves. The Ball/Egg/Peg with Cup makes a great first puzzle for a baby as it offers a variation of the development of the palmer grasp and the co-ordination of both hands together.
These toys are ideal for children around 9 months because at this age they are naturally interested in fitting things together which also improves their cognitive skills.