I lived in Waynoka for several years, and I can attest to the heat and wind during the summer. Having spent two tours in the sandbox (Iraq and Afghanistan), I can tell you it's nearly as hot on the dunes as over there. It's no place for kids during the summer. As I mentioned, the wind is a factor, too. Being so low to the ground, they'll get sandblasted much easier, and it will be a trip they'd rather forget. Believe me, the wind can sandblast you. It'll blow up to 25-30 mph sustained at times. Stick to the south campground, too. The north campground and Cowboy Camp can get rowdy at times because the rangers have to travel to get there. Their office is the first thing you meet when approaching from the south, so they can keep order there easier. I would suggest the fall instead of the spring. Even though the most severe weather is usually near central OK, NW OK gets its fair share. May is very active almost everywhere in OK. During the fall, the days are milder, the winds are calmer, the sunsets are gorgeous, and the nights are chilly enough for a campfire. All of those combine to make wonderful memories for the kids. Enjoy your trip.