It depends on what your relationship with your ex is. I don't know you or him but to walk out and pay you nothing for 19 weeks is kind of the one sticking point that makes it clear you need to just dot your i's and cross your T's and use the legal avenues to ensure that your children are supported.

I am curious, whilst he paid yo nothing for 19 weeks did her make time to see his children regularly or did you have to chase hi down the street to get him to see them?

If he is an interested and committed father he will not only want to see his children but to support them and to maintain some kind of relationship with their mother.

So all in all I would be using the legal system for what it is set up for and ensure all arrangements are in writing.