As an appaloosa owner, and knowing a few appaloosa breeders, they in general, can be great kids mounts and riding mounts with proper training just like any other horse.
My friend's 8 year old appy can be trusted with a kid's life. But then, there are some that are the typical spooky horse. I would just get to know the horse better =) to make sure she wouldn't do anything. But giving the circumstances she's 15, been rode alot (assuming since the horse was a favorite) I would say she probably is kid safe and has been trained really well.
Lettin' the cat outta the bag is a whole lot easier than puttin' it back. -- Unkown