A: Peter, although many babies remain safely in their cribs for two years or more, babies who are physically active and driven to explore, like your son, often climb out of cribs earlier. The basic rule is: Once your son has tried to climb out of his crib, it's time for a safer sleeping arrangement. The fall from the crib probably scared him as much as it scared you, and he may take a break from his climbing adventures, but he'll probably do it again soon.

Have you done everything you can to prevent him from climbing out of the crib, such as lowering the mattress to the lowest setting to make the bars as high as possible, and taking out the crib bumpers and stuffed animals that he might use to step up on? If so, it's time that he graduated from the crib.

Knowing that your son likes to climb and explore, it's probably safest to put him in a mattress on the floor. That way, if he climbs out, he won't fall far. You can get him a toddler bed or go directly to a regular-sized twin bed mattress. It might be helpful to put a guardrail alongside the mattress on the floor, so he gets used to sleeping with the rail.

Be sure to show him that you expect him to stay in his bed at night. But also childproof his room by securing or hiding lamp cords, covering electrical outlets and removing furniture from near the windows, where he could climb. Also consider adding a baby gate across his door to prevent him from wandering throughout the house.

When he turns 2, explain to him that he's ready for a big boy bed, and put the mattress up on the box spring and frame, with the guardrail. Take some time to teach him how to get down from the bed safely by sliding down on his tummy. Hopefully, you'll never have to hear another thud.