Oh I totally feel this! What worked for us was using Screen Time in Apple’s settings - you can set downtime schedules and it’ll automatically lock the device at bedtime, plus you can manage it from your own phone once you set up Family Sharing. That said, I actually switched to Eyezy because it gives me way more flexibility to remotely control screen time across all their devices in one place, and I can shut things down instantly if needed without all the Apple setup hassle.