The first step, before adding your child’s Facebook account to “Avira Social Network Protection”, is to create a personal account on "Avira Social Network Protection".
How do I create an account on "Avira Social Network Protection"?

If you have successfully created an account or you already have an account for “Avira Social Network Protection”, then connect your child’s Facebook account to the “Avira Social Network Protection”.
How do I add my child to "Avira Social Network Protection"?

In case you do not know your child’s Facebook credentials, but still would like to connect their Facebook account to “Avira Social Networks”, read the following article.
Can I use "Avira Social Network Protection" if I don't have my child's account passwords?