Glacier Nat Park

WE are planning on going to glacier mid July, about the 17th. How quickly do I need to book my sites, should I already be booking? We are going to be in Waterton July 13-17 and then heading to glacier after. Do the campgrounds in the park have power, and playgrounds? Or doo I need to stay at a KOA to get that? I can live without power, but traveling with a 4 and 6 year old makes having a playground a necessity.