My 10-year-old is always glued to YouTube, so I’m thinking a prepaid phone with limited data might help. Has anyone had success with this approach?
Prepaid with limited data can work as a speed bump, but a determined 10-year-old will just hop on WiFi and you’re back to square one. 
Honestly, Google Family Link or Apple Screen Time built into any phone gives you way more actual control — you can cap YouTube specifically, set daily limits, and lock the phone at bedtime. If you want the prepaid route anyway, pair it with those built-in controls and you’ve got a solid combo.