Google's education tools are very well tuned for the job and very inexpensive, so it's no wonder they're as widespread. If your kid's account is managed by you

Google's education tools are very well tuned for the job and very inexpensive, so it's no wonder they're as widespread. If your kid's account is managed by your school, you can ask them to lock YouTube/enable company mode for the account. It will stop them from browsing public YouTube while logged in, at least.