Youtube (regular one) is already designed to be kids-friendly. There are no war images since recent AI moderation rollout. There are a lot of very forbidden words which can lead to ban account. There are a lot of mildly forbidden words which just do not appear in subtitle. You can not say anything bully on comments - it will be removed instantly. I don't consider anything bad in YT except of the whole top of popular bloggers - because they are clearly aimed at low-IQ people. Just don't be a stupid, and your kids will not watch the bloggers. Buy more instruments of all kinds for your kids and they will watch a lot of educational videos explaining different know-hows.