Any ideas on how to toddler proof the crib?

Ki

I put my 5 month old down for a nap in his crib and my 2 1/2 year old in his bed. (Same room). About 5 minutes later, I hear my 5 month old crying and my toddler is in the crib with him. He could pick my baby up so that scared me bad. Has anyone else had a similar problem? At this rate I probably won’t have them sleeping in the same room until my baby can stand on his own.