Wait... I don't generally recommend any objects in the crib except your baby. If you must i would at least wait until over one year in age, probably closer to two years. After one year the risk of sids is greatly diminished but i would recommend a longer period of time.
Stuffed animals. It is usually safe to have a stuffed animal in the crib at 6-7 months. Make sure the stuffedanimal is not to small so the child could choke on. Also make sure that there no small attachments sewn on the animal like eyes or buttons. Another consideration is if your child is allergic furry animals might cause running nosesand cough.