It used to be that toting a child in a stroller past the age of 3 was the exception to the rule, but it’s rapidly becoming the norm. For parents of infants and toddlers, strollers are one of those indispensable items on their equipment “must have” list. Some can’t imagine a family trip to the zoo or airport without taking a stroller along. But experts say once a child is able to walk proficiently, typically between the ages of 2 and 3, overusing a stroller can interfere with physical development.