Family Reunification Visa - renewal question

[wheatism]

UK citizen with a young German son (living mostly with his German mother).

I'm here on a family reunification visa which is up for renewal next year (they are valid for 3 years at a time). Can I just keep renewing every 3 years or does the family reunification visa only apply for a 'dependant child' and what age does that no longer apply; when the child is 16, 18, 21?

I'm studying for B1 and hence aim to get permanent residency but my language learning is going slowly!

[LeonG]

I know someone who is on a "parent of German child visa". She initially got 3 years, then another 3, then 5. As far as I know, you can continue on this visa as long as your child is a minor, that is under 18.