Father of three kids (8, 6, and 19 months) here. We took more or less an “attachment parenting” approach with ours; my wife is a proponent of extended breastfeeding, and that’s a whole lot easier to do when the kid is in the bed with you already. Our oldest, now 8, self-weaned at about eighteen months when my wife became pregnant with our second – apparently, the hormonal changes caused enough changes in the breast milk that he was put off by it. After that, he slept in his own bed; we would read to him before bed and I would often sit on his bed or even lie down with him (he was sleeping on a futon, only about 12 inches off the floor, with lots of room) until he fell asleep. Once he got to be three or four years old, we got to a point where we would do our bedtime ritual, and I would usually stay in his room for a few minutes after lights out, but not necessarily until he went to sleep; about half the time he would still be awake when I left. By the time he was five, it was down to saying goodnight and leaving him to go to sleep on his own. Ever since he moved to his own bed, he’s pretty much stayed there – I can easily count the times he’s climbed into bed with us since then.
My first daughter, now six, also self-weaned at about eighteen months – in her case, she just seemed to lose interest. Again, once she stopped breastfeeding, we moved her into her own bed, and through the same sort of process as with my son, she’s now at the point where she can easily get to sleep on her own, though she still prefers for my wife to sing her a goodnight song that they’ve come up with first. She’s much more likely than my son to climb into bed with us, but that seems to be largely because she’s such a light sleeper – once my son’s asleep, nothing wakes him up, while she wakes at the slightest disturbance. She’ll usually go back to her own room, however, if you ask her to.
My younger daughter is still breastfeeding at 19 months, and is still co-sleeping. I expect that once she stops nursing, we’ll move her to a bed of her own in the same room with my other daughter.
Overall, my impression from conversations with other parents is that ours seem to have fewer problems going to sleep and staying asleep on their own than the average, but that’s an impression, not a scientific conclusion.
Most of the arguments against co-sleeping and other attachment parenting tactics are either patently absurd (kids being injured by a parent rolling over on them? please – how many times have you accidentally rolled out of your bed in your adult life?) or boil down to a contention that because some parents aren’t able to deal with it, it’s inherently wrong for everyone. Every kid is different, and every pair of parents is different, and what’s right for each set is likely to be different as well. I wouldn’t tell another parent that putting their kid to bed and letting them cry it out is necessarily wrong, or that they should do things the way we did – it worked for us, but wouldn’t work for everyone.
Short of doing video-based sleep studies of children and correlating those results with the parenting style of their parents, I don’t know that you’d ever get an “factual” data on this, and even that would only deal with sleep-related issues, not other behavioral information. Other behavioral stuff would be so subjective that it’d be very tough to come up with definitive measures.
