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.
As your baby gets used to tummy time, place your baby on his or her stomach more frequently or for longer periods of time. For a 3- to 4-month-old baby, some research suggests aiming for at least 20 minutes of tummy time a day. Remember, however, to never leave your baby unattended during tummy time. If your baby becomes fussy or sleepy during tummy time, change his or her activity or place your baby to sleep on his or her back in the crib. With. Jay L. Hoecker, M.D. 1  Starting solids. 2  Vitamin D for babies.