YouTube Kids is good for under-7s. Past that, kids move to regular YouTube — and the real work is configuring it properly, because "just use the Kids app" stops working.
Follow our Android/Chromebook guide to create a supervised Google account. YouTube inherits supervision from the Google account.
Family Link → child → Controls → YouTube. Three options: Explore (ages 9+), Explore More (13+), Most of YouTube (teens). Pick one age band down from your kid's actual age.
YouTube → long-press a video → Don't recommend channel / Block. The algorithm really does listen to this over time.
Profile → Settings → General → Restricted Mode → On. It's per-device and per-browser, so repeat on every place they sign in.
Same menu → Autoplay → Off. This is the #1 time-sink fix.
YouTube → Library → History. Once a month. Less about surveillance, more about "what have you been into lately?"
Profile → Settings → General → Play Shorts on Home → Off (where available). Shorts are the most algorithmically aggressive part of YouTube.
For kids under ~10, hide the comments section entirely: via browser, with the Hide YouTube Comments extension, or just skip-past them as a habit.