When we first went vegan we got a lot of heat from our family and lame comments like you describe.
Over time I got a lot better at "defending" our diet and lifestyle and no one can argue with the fact that my child is very healthy and so are my husband and myself.
Now when people say, "How do you get enough protein?" I say, "How do you avoid getting too much?"
And, "Aren't you depriving your child by forcing her to be on a vegan diet?" and I say, "Yes, I'm depriving her of heart disease, cancer, obesity, diabetes, stroke, high blood pressure, etc. etc."
You get em girl!