How to change an Apple ID Account type?

Hi There,

I have a questions and would like a clear answer.

Here's the scenario. A while back I decided to give one of my iDevices to my now 4 year old son. Instead of putting it under my AppleID, I created one for him but not as a child, but rather as an adult. Recently I started the family thing on Apple IDs and seems pretty cool. So I setup another of my old iDevices for my other now 3 year old son. When creating the account, I noticed there was now an option to create an account for a child. I really like the way it works. No accidental in-app purchases, no extra work on my part for device restrictions, no hassle.

Here's where I need help. I want to convert/change my first son's account from an adult type to a child type. they don't use email, and all paid apps would be purchased by me anyway. I don't want to change his Apple ID username, just change it's type from adult to child.

Would be nice to just delete the account and recreate with same ID, but I keep seeing messages saying accounts cannot be deleted.

So, the most important thing to me is that the AppleID for him remains the same. Now, the deceptively simple question is how do I change the account to have the same AppleID but become a Child account instead of Adult account.

Thanks.

A Dad.