According to the American Association of Pediatrics (AAP), Before your baby turns 12 months of age, you shouldn't put a blanket or anything soft in their crib because it can increase the risk of accidental suffocation.  A blanket can also cause your baby to overheat, which is another risk factor for SIDS. You should only place a snug, fitted sheet over a mattress that will fit the crib and no other bedding should be included. Make sure nothing is hidden under the fitted sheet.