Ugh. Minecraft. When Microsoft bought this, they ruined everything. Trying to set up an account so your kid can play with other kids online is such a hassle. Don't even bother with the kids account, you will regret ever doing it. Just set them up as adults and thank me later.
Now. Let's try and play Minecraft on a different platform like the switch. Good luck. Once you associate one Minecraft user to the switch you are pretty much screwed at that point. If you have more than one kid sharing the switch, the user doesn't change when they select their profile to play the game. It's terrible. I still haven't figured out how to change minecraft users on the switch and I could care less. It's not worth the stress and aggravation.
If only one kid uses the switch, you'll be fine, more than one, don't bother buying this game.