For families whose youngest children are elementary-, middle-, or high school-aged, a sense of never having enough time to get everything done leads some to buy extra-large, family size, and even industrial size packages of products. And they prefer so-called "big box" and warehouse type stores, like Costco and Sam's Club. They like big packages and big stores because they help decrease their number of shopping trips. These families who don't have enough time are prevalent in which stage of the family life cycle?