Gonna need few more details on that.
When you say over kids is it that one of you wants them and the other doesn't?
If so, that doesn't typically change and it's a MASSIVE thing. Like as far as deal breakers go, no matter which side of the fence you are on, this is one of those that I think is completely reasonable.
People do change their mind sometimes but its not something either side should really wilt on. Like if someone truly wants kids, they shouldn't have to forego that to be with someone (I've seen this before, it was basically poison for the relationship.) On the flip side, if you don't want them you shouldn't have to force your self to do it. It's a massive commitment to raise another human and it isn't something you should have to "learn to live with" - these people generally make pretty shitty parents, not to mention that it would make you miserable.
If you want a chance to make amends for not ending things the right way, I'd say reach out and see where it goes but don't push it if she isn't interested. If you want to rekindle the relationship and what I wrote above is accurate, I'd strongly suggest that you not do that. You may quell the shit you're feeling right now but what broke you up to begin with would still be an issue and when it rears its ugly head again, its going to hurt so much worse.