Jumping in here because I tried a bunch of apps before landing on what works and I can save people some testing time.
Tried: Kids Place (Android) - it creates a launcher that locks kids into approved apps only. Works okay for young kids. But a factory reset removes it completely. If your kid is old enough to google how to reset a phone, this one is not your answer.
Tried: OurPact Free Version - gives you one app blocking schedule per day on the free tier. Very limited but it does work and cannot be easily uninstalled because of how it handles device admin. Paid version unlocks way more scheduling options.
Tried: Bark Free - does not block content, it monitors and alerts you to concerning messages or searches. Different purpose but worth knowing about if you want a light touch approach for older kids.
Tried: Google Family Link - currently using this and it is the one I stuck with. The approval system for apps is really what makes it stand out. Nothing installs without me seeing it first.
Bottom line: there is no single perfect free app. What works depends on your kid age, their device, and how much you want to manage it actively. Family Link is the best all around free option for Android right now in my experience 