A computer carton or other large box can introduce your baby to the concepts of "inside" and "outside" – and also provides the perfect secret hideout.

Appropriate for: 8 months to 1 year
Skills developed: Gross motor, spatial relations
What you'll need: A sturdy cardboard box big enough for your baby to fit in

Put a soft blanket and some toys and books in the box with your baby and let him or her explore this new little space. Cut windows out of a tall crate and you've created a play house, where your baby can play peekaboo with you and get that first deliciously powerful taste of "no parents allowed." Another option: Turn a large box on its side and let your baby move in and out at his or her leisure. Safety note: Never leave your baby unattended in the box, as it could tip over.