How to make an Apple ID account for my child?

So it does seem that you want to setup a child account for your child.

First I would recommend to setup family sharing https://support.apple.com/en-us/HT201088

After you setup Family sharing, you should be able to tap "add member" then select the option for a child.

This resource will help you after you setup family sharing https://support.apple.com/en-us/HT201084 "create an Apple ID for child"

hope this helps ;)

If 13 years old or older.

Apple ID - create a new.      

Apple ID – Create         

If under 13 years old, you will need to set up Family Sharing to create an ID.

Family Sharing and Apple ID for your child.      

Family Sharing.         

Family Sharing - Set up.