Move From a Crib to a Bed
Try it at 2 to 3 years I would suggest keeping little ones in a crib for as long as possible because it’s a secure environment. Most kids can safely remain in their crib until 2 or 3 years of age. You’ll know that your child is ready to graduate when she starts trying to climb out of her crib or use it as gymnastics equipment.
Smooth the transition If you’re ready to move your child to a bed, you’ll want to make sure her room is totally kid-proof. The key here is totally. That means if you have a cute bookshelf in the room, it needs to be fastened to the wall so she can’t pull it onto herself. Also make sure all power cords and drapery cords are inaccessible. If the rest of the house is not completely child-safe, either lock the bedroom door or install a security gate in the doorway to make sure your toddler stays put until you come and get her.
We had just one crib and never attempted to put the gals in the same crib for a simple reason that they might hurt each other. We used to keep each child in the crib every alt day so that they get equal chances.
PS- these tips are based on my experience. Can vary from child to child.