Over the years I've had a bunch of parents ask me to help with with the issue of content moderation for their children to help make sure they don't wind up going to internet sites with sexual or violent content, and to set time limits for certain apps or general usage. A friend of mine has been using Kidslox to set time limits and content filters for his son and he has been really happy with it.
Kidslox is a subscription based service built on an app that is installed on both the parents' and childs' devices. The parents can set limits and change those parameters in real time if needed and it works on iOS and Android devices. There are a number of solutions in this market, I recommend you check them out and see what solution is right for you and your child(ren). If you need help setting it up, get in touch.