1 to 3 months
What Your Baby Learns: He's starting to grasp that people and things exist, and they are separate from him and from each other. He'll be able to follow moving objects that are close by, and identify where certain sounds -- such as your voice -- are coming from.
Brain Boosters: Place a mobile over his crib, put him tummy-down on a gym mat to play, and let him look into a nonbreakable mirror: He'll be captivated by anything that moves. At around 8 weeks he'll start to notice checkerboard patterns.
Keep in Mind: Toys with lots of lights, bells, and whistles probably won't be much fun for a baby at this age, so keep playthings simple. Competing noises (such as a vacuum cleaner and the stereo) may also stress him out.