How to make this app invisible on my kid’s phone?

It is impossible to do so, and is prohibited by Google and Apple policies.

Based on our experience, it is better to explain children the purpose of the app. You can tell your kid that it is the app for watching parents as well.For example, your kid will know where you are, when you get home and he/she will be able to restore order or to say goodbye to friends before you come. Kids will appreciate this.