This is a hobby horse of mine to the point that coworkers probably wish I'd just stfu about Minecraft - but holy shit is it crazy how many different things you need to get right to get kids playing together.
I genuinely have no idea how parents without years of "navigating technical bullshit" experience ever manage to make it happen. Juggling Microsoft accounts, Nintendo accounts, menu-diving through one of 37 different account details pages , Xbox accounts, GamePass subscriptions - it's just fucking crazy!
Getting an actual kids account to work online with minecraft involves setting the right permissions across 2-4 websites and 1-3 companies. I think it took me around 4 hours of trial and error to get it working.
I'm essentially the maintainer of a series of accounts for each kid, these days. Woe unto anyone without a password manager!