In trying to put myself in your shoes, if I was getting a number of people commenting on how I teach my child, I might start by questioning myself and ask a friends/family/expert/teacher-(someone I trust & who has seen me teaching my child) if there is something that I might not be aware of that might cause people to comment on my teaching. If this honestly turns out to be a definite no, then I would think about saying something like what is mentioned in other comments to the effect of, "thank you, I have worked this out to be the best method", and then shift your attention to your child. When you give someone your attention, that leaves room for them to continue comments, so I would keep it short and like already mentioned, return to teaching your child.

In trying to put myself in your shoes, if I was getting a number of people commenting on how I teach my child, I might start by questioning myself and ask a friends/family/expert/teacher-(someone I trust & who has seen me teaching my child) if there is something that I might not be aware of that might cause people to comment on my teaching. 

If this honestly turns out to be a definite no, then I would think about saying something like what is mentioned in other comments to the effect of, "thank you, I have worked this out to be the best method", and then shift your attention to your child. When you give someone your attention, that leaves room for them to continue comments, so I would keep it short and like already mentioned, return to teaching your child.