I don't disagree. Young horses can rear as their first reaction. After some good training...it should go away. If it goes away and comes back...and takes are REAL expert trainer to "get it out" of them....then that points to pain to me.
It may not be curable. And I would NEVER lable them as a kids horse. But in all honestly....I'd NEVER sell ANY young horse as kid safe. They are a young horse. No matter how well mannered they may be with me...put a less experienced rider or handler around them and that may be out the window quickly.
Things were said to this OP that I would never say to them really about any horse.