...Don't let the haters get to you.
I think the last part is key, pretty much for any vegan in any situation. I understand taking attacks / ignorance personally – it is so hard not to, especially when it comes to the welfare of your child. And I sure identify with the desire to be able to “win an argument” with a meat eater. But the reality is that there are some people who will be belligerent regardless of what we say.
I think we will all be happier – and thus better examples, and thus better advocates for the animals – if we accept that some people will just be jerks. (And let’s be honest – that’s true about vegans, too – there are vegans who will be loudly belligerent with anyone whose thoughts deviate ever-so-slightly from theirs.)