Safety: A child's own bed is a safe place for them to sleep, free from the risk of being rolled on, suffocated, or injured by their parents. A separate room also helps to reduce the risk of sudden infant death syndrome (SIDS).
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Sleep quality: Children who sleep in their own bed tend to get a better night's sleep than those who share a bed with their parents. This is because they are less likely to be disturbed by their parents' movements or noise. A separate room also provides a darker, quieter environment, which is conducive to sleep.
Privacy: As children grow older, they need more and more privacy. Having their own room gives them a place to relax and be themselves, away from the prying eyes of their parents. This is especially important for teenagers, who are developing their sense of identity and independence.
Of course, there are some cases in which it is necessary for a child to sleep on the couch. For example, a child who is sick may need to sleep close to their parents for monitoring purposes. However, this should be a temporary arrangement. As soon as the child is well, they should return to their own bed.
In conclusion, the AAP recommends that all children have their own bed in a separate room from their parents. This is for a number of reasons, including safety, sleep quality, and privacy.