Look I am going to push back on something here. Everyone in this thread is talking about apps like they are the solution to parenting and I think that is a problem.
These tools, whether free or paid, work fine technically. Yes Family Link does what it says. Yes Screen Time on iPhone is solid. But here is my issue: what happens when the kid gets a different device? A school tablet? A friend phone? A gaming console with a browser?
You cannot install Family Link on every screen your child will ever touch. So if the only reason your kid is not watching inappropriate content is because of an app on their phone, the moment they get any other device that protection disappears.
Also let me bring up something nobody wants to say: a really motivated teenager will find a way. They will borrow a friends phone, use a VPN, or find whatever workaround is trending on YouTube this week.
I am not saying do not use these apps. I am saying use them as one part of a bigger approach that includes actual conversations with your kids about why certain content is harmful.
The app is a fence. Fences can be climbed. You need to also teach your kid why they should not climb it 