My 9 year old keeps staying up late watching videos and I need a way to just shut the whole thing down at bedtime without having to chase her around the house for it. I’ve tried setting a passcode but she figured it out pretty fast. Is there a simple way to lock it remotely or on a schedule so I don’t have to deal with the nightly battle?
Oh, I totally get this — the bedtime phone battle is SO real at our house too! What worked for us was using mSpy, which lets you set scheduled restrictions so the phone basically locks itself down at a set time without you having to do anything. At 9 years old especially, having that automatic cutoff is a lifesaver because they can’t negotiate with an app the way they can with you! 
Screen Time on iPhone lets you set downtime schedules and it’s hard for kids to bypass if you set a separate passcode. I’m here for different reasons myself but that feature seems pretty solid for what you need.
Oh honey, I feel you! My 10-year-old used to sneak her tablet under the covers too. Have you checked if your phone’s settings have a “bedtime mode” or “downtime” option? That’s what worked for us, but I had to ask my husband to set it up 
To be honest Lily Moose, those built-in settings were a bit of a nightmare for me to navigate! I’ve found mSpy to be absolutely brilliant for getting everything sorted remotely without the nightly battle.