How to approve Roblox 'ask permission' request sent to parent on iPhone?

My son tried to download Roblox and send message ask permission request sent to parent. where do I did this and approve to load the app. I get it in my messages but do not know how to approve

[Re-Titled by Moderator]

Original Title: My son tried to add Roblox and says ask permission request sent to parent. where do I did this and approve