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Lower the crib mattress to its lowest setting and remove anything your toddler could use as a step, and keep bedtime calm and predictable. The American Academy of Pediatrics (AAP) says once your toddler can climb out of their crib, it may be time to move to a "big kid" bed. The AAP also recommends switching once your child is 35 inches (89 cm) tall, or when the side rail is less than three-quarters of their standing height.