OK, I'll take the thread in a slightly different direction....
When I started in Rockets with my kids, I made the mistake of following in Tim "The Toolman" Taylor's footsteps - "Mo' Power!". I bought rockets for the kids based on the altitude on the package - "That one only goes to 500 feet, this one goes to 750 feet!". Guess which one we bought?
Looking back, the kids just wanted to build a rocket, and be able to watch it launch, pop, and land. I wanted to build the fastest, highest rocket. Unfortunately, my choices led to too many launches where we lost sight of the rocket until maybe we could see a puff of smoke when the ejection charge went off, or maybe someone would catch sight of it as it floated down to the ground, or maybe someone would catch sight of it as it drifted into unrecoverable areas. My suggestion is to build fat rockets - they don't go nearly as high, so they're much more entertaining to watch, and they don't drift as far downwind. Don't automatically reach for the 'C' engine just because it fits in the rocket - prefer the 'A' or 'B' because they keep the rocket closer. Keep the 'C' for wide-open spaces on rockets that you don't mind losing. I still have a tiny little kit in the bin to be made someday called the "Cee-Yah", that has a tag line on the instructions of "Put a C Motor in it and say CEE-YAH!". Not really what you want to start the kids out with.