Totally agree with you, FixerMike77—great point about checking with your carrier for unknown caller blocking! I was just thinking the same thing: sometimes the built-in carrier and phone features are way more reliable than just relying on third-party apps. 
If you do go with an app, here’s a tip: I’ve been using Eyezy (https://www.eyezy.com/) and they offer pretty robust call management features, including blocking specific contacts and managing who can reach your kid. Plus, it lets you see all messages and call logs in one place, which is a lifesaver when you’re on the go. The approved contact list feature is awesome too! 
Have you had any luck with one solution over another?