NookLink with a child account

I want to use the NookLink features in the Nintendo Switch Online mobile app with my child's account.

When I sign in on the NookLink I see my adult account and the child. When I select the child account it says this cannot be used.

When I choose the adult account and select Animal Crossings : NH under settings it shows a change players. I only see my account there too.

Here is the deal. My child will play online with a friend and spends way too much time typing out chats. I want here to be able to use a mobile device to type and send messages.

How do I use the Nintendo Switch Online app with a child account?

From Nintendo's FAQ:

Yes. Any Nintendo Account associated with the family group can use the Nintendo Switch Online Family Membership. Parents may use Nintendo Switch Parental Controls to set restrictions.

Nintendo Account holders must be age 13+ to use the Nintendo Online Service smartphone app; restrictions for this app can be managed with your smartphone's parental control restriction settings.

If the child account's age is set to less than 13, they're not going to be able to use the voice chat features.