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.
I want to reiterate that initially putting baby to sleep on his back is the right way to go, even when they start rolling over on their own later. A recent study revealed that as many as a third of full-term infants are not placed on their backs to sleep, and the number was even higher for babies born prematurely.