The mobile hanging above the crib is an essential part of any dream-nursery, but like crib bumpers and pillows and blankets, there is much debate about whether mobiles are safe. The AAP and other organizations have come out strongly against bumpers and other items in a young baby's crib, so is the mobile the next thing to be eliminated in the transformation of the crib? Or is it one of the only safe holdovers from your dream-nursery?
There are two main schools of thought about having mobiles in cribs, and what they do to your baby’s sleep. Both ideas sound plausible, and both were developed as a way of working towards a goal that’s near and dear to your heart - encouraging your baby to sleep through the night. Unfortunately, these two schools of thought completely contradict each other - there isn’t really an opportunity for a happy medium.
Fans of crib mobiles argue that they entertain babies when they wake in the night, which means that they’re willing to wait for you more patiently if it takes you a little longer to get to them. The theory suggests that if they aren't waking up for a feeding or a change, but rather just for the sake of waking up, they might be distracted enough by it not to end up calling for you at all.
On the other hand, the argument against the mobile is that it can transform babies’ associations with their cribs from places to sleep to places to play, which could make it harder for them to fall asleep. In the end, it may come down to a question of your baby’s personality, whether a crib mobile will help or hurt her sleep. In either case, in the first few months, as long as the mobile is securely attached to the crib or ceiling so it won’t fall down into the crib, and all of the hanging pieces are both securely fastened and fastened on strings no longer than 7 inches, mobiles don’t present any danger - besides the danger to your sleep schedule that your baby might be one of those children who likes her mobile enough not to want to fall asleep when it’s around to watch!
The only point when the mobile starts to present a safety hazard is when your baby is around 5 months or whenever she starts sitting up. This is when she starts getting close to being able to reach up and grab things, or sit upright. Even if your baby isn’t quite at that point physically, when her fourth month rolls around, it’s a good idea to move the mobile preemptively. After all, she will be mobile enough to start going after the mobile soon!