Child's gamertag missing from parent's Privacy & Online safety settings

Experiencing the same issue as reported in this
thread.

In summary, I've setup an XBox Live account for my son from Minecraft PE on an iOS device. He already had an existing child account in our family Microsoft account but his gamertag isn't appearing in Privacy & Online Safety settings
screen from my parent profile, which is preventing me from changing his settings to resolve the issue: "You cannot play on Realms because of how your Microsoft Account is setup. This can be changed in your privacy & online safety settings on aka.ms/accountsettings."

I really don't want to create him a completely separate child account in our family Microsoft account just to play Minecraft safely.

Any help in rectifying this would be greatly appreciated.

:)