London. It depends when one applied. If you were already there and it was by 30/6/21 then you would have been handled normally under the Withdrawal Agreement, if after, you are able to rejoin on a family reunion visa by dint of having a German child - with no language requirement - but that still isn't permanent residency. All that said, there appears to - still - be some lack of clarify between various government departments on this front. Not sure why, because the UK is now a third-country and that should be the end of that.