Did a little boy a great favor today at the park.  I was there with my two little charges - one who will soon by 5 and one who is 3 1/2.  This little boy's dad was happy that we showed up because his son, Carter, is an only child and they like for him to have interaction with other children.  He is four, so right in between my two.   Dad started a conversation with me, and we chatted about kids of that age and found that they were all in pre-school part time.  Got around to the fact that Carter won't sleep in his own bed at night.  I told his Dad that it was only natural for babies to want the protection of their parents at night. Other species don't leave their children unguarded and vulnerable.  If an infant of another species gets lost and finds itself alone, it howls and howls until Mama comes to fetch it home.  Humans are the only stupid ones.  The conflict comes when Dad wants Mom all to himself.  In other countries the family sleeps  together and I guess the kids just know about sex.

Here is a quote from Wikipedia on the subject:

One study reported mothers getting more sleep by co-sleeping and breastfeeding than by other arrangements.

It has been argued that co-sleeping evolved over five million years, that it alters the infant's sleep experience and the number of maternal inspections of the infant, and that it provides a beginning point for considering possibly unconventional ways of helping reduce the risk of sudden infant death syndrome (SIDS).

Stress hormones are lower in mothers and babies who co-sleep, specifically the balance of the stress hormone cortisol, the control of which is essential for a baby's healthy growth.

In studies with animals, infants who stayed close to their mothers had higher levels of growth hormones and enzymes necessary for brain and heart growth.

The physiology of co-sleeping babies is more stable, including more stable temperatures, more regular heart rhythms, and fewer long pauses in breathing than babies who sleep alone.

Co-sleeping may promote long-term emotional health. In long-term follow-up studies of infants who slept with their parents and those who slept alone, the children who co-slept were happier, less anxious, had higher self-esteem, were less likely to be afraid of sleep, had fewer behavioral problems, tended to be more comfortable with intimacy, and were generally more independent as adults.

However, a recent study (see below under precautions) found different results if co-sleeping was initiated only after nighttime awakenings. Co-sleeping from birth or soon afterwards is the norm except in some Western cultures.

I hope that my assurances that he was not "spoiling" his son, nor was he keeping him a baby, helped that Dad have more confidence in his and the mother's decisions to let Carter sleep with them if he needs to.  He will outgrow that need just as the young of every other species do.