With our full size cribs and most of the mini crib, you are able to adjust the mattress height; some have three levels, some have more. The higher levels make it easier to take your infant out of the crib, but they're dangerous when your child is able to pull herself to a standing position. Before your child reaches that stage--about 6 months--the mattress should be at its lowest setting. Bumper pads and large toys can help your little escape artist climb out, which is another reason they don't belong in the crib.
Place your baby's crib away from windows, window blinds, wall hangings, curtains, toys, and furniture so that he can't get to anything dangerous. Make sure any baby monitors (and cords) are also out of reach.
For safety's sake, watch your child's development closely and stop using a crib as soon as he can climb out. At that point, consider a toddler bed with child railings or put the mattress on the floor. Don't put your child back into the crib after the first "escape," regardless of his age. A child attempting to climb out of a crib can fall and be seriously injured.