Our baby is growing up! (and out!) After too many blowouts this past week, we concluded the newborn size diapers might just be a bit too tight and we moved Spencer up to size one over the weekend . So far, so good. Plus, unlike newborn size, size one diapers are available at Costco and can be purchased hundreds at a time. Saturday's haul of a giant box of diapers plus a giant box of wipes should keep us well-stocked for about a month.