He's a not a 'mean girl' ffs. That's massively downplaying this.
He's a bully. Like most bullies, his behaviour had been enabled and encouraged by unpleasant people who find it amusing (when it's not directed towards them).
He doesn't understand how his words affect me, no matter how i try to explain it
He DOES understand OP. He simply doesn't care.
Bullies, abusive, twisted, sadistic, or narcissistic people are like that. They are low in empathy and take a sadistic pleasure in cruelty, in upsetting others. Some of them have low self-esteem and enjoy taking others down a peg or two in order to soothe or puff up their own egos or sense of self-worth.
@WitcheryDivine She can try, but it likely won't work. This behaviour is deeply ingrained and comes from the fact he knows the effect it has on people - that's why he does it!
Most of the time i ignore him, sometimes i poke fun back but other time it does really hurt and I go away and have a little cry
I feel sorry for you, that you' haven't had the emotional support or guidance to recognise this behaviour sooner, before you had children with him. I also feel sorry for his child, and they too will likely mimic this behaviour and be subject to this emotional abuse themselves.
OP, there should be no need to ignore a partner, or resort back with similar jibes, or defend yourself in some way. Such a man is NOT on your side. I'm wondering if you even know what that feels like.