asÂ·soÂ·ciÂ·aÂ·tive property. The property of addition and multiplication which states that a difference in the grouping of numbers being added or multiplied will not change the result, as long as the order of the numbers stays the same. For example, 3 + (4 + 5) is equal to (3 + 4) + 5. See also commutative property, distributive property. 1  Facebook.
The most common recommendation is to initially place infants to sleep on their backs for the first 12 months. However, when the infant is able to roll over on their own in to the sleep position of his/her choice than it is fine to leave the baby in that position. My children are now 29, 27, 24, and 11.
However, it has also saved thousands of lives, and rolling over later is not a serious enough reason to not put a baby to sleep on its back. Infants used to roll over from front to back at about 4 months, Dr. Olson says. It currently seems more common to see this at 6 months. There are no apparent consequences to this slight delay.. If babies aren't rolling over by 12 months, he says this should prompt some additional attention from the pediatrician.