What is called "co-sleeping"–kids sleeping in their parents' bed–is popular today among a small minority of very devoted parents who passionately believe that young children need close bodily contact with their parents. Nearly every family admits to occasional co-sleeping. Whenever there was a thunderstorm in the middle of the night, my husband and I could expect two frightened toddlers and a frantic Schnauzer to join us.

Most parents allow young children into their bed, at least on occasion. 92% of middle-class US families report taking a sick or frightened child into their bed. About 60% of these children go back or are taken back to their own bed within a half hour, another 31% stay in the big bed until they are asleep, and only 1% stay the rest of the night.