When DD#2 was little, DH and I were separated for a little over a year. (DD#1 has a different father, so she is not in this equation, as DH didn't have parental rights to her at that time).
Our verbal agreement for DD#2 was: DH pays for insurance and all medical bills; 1/2 of daycare costs for her normal 2 days a week; buys what she needs when she was with him; and he had her on his 3 days off (worked a 4 day workweek, 11 hours a day). I paid for her things she needed when she was with me and 1/2 daycare costs. He made about twice what I did, so we thought it fair he covered the medical portions.
I worked 5 days a week, 3 of which were his days off--so he was only paying for childcare for 1 day a week due to both of us working, and I paid the other.
When he started grappling on his days off, it was up to him to find her childcare and pay for it. If he was sick, it was up to him to find her childcare and pay for it. If I was sick, it was up to me to find her childcare and pay for it.
Amazing what two adults can work out, if both are being mature and sticking to the plan...
On the other hand, DD#1's father never paid his child support (had to go to court to get it ordered, because he refused to try to work out any kind of arrangement with me). He would work a job for 3-4 weeks, then quit, so that the court wouldn't have time to garnish his wages for cs. He lived his dad for awhile, and then his mom, and would take DD1 to their house for his visitation, and leave her while he went off to play. They got tired of it, kicked him out, and he bounced from house to house--and expected me to let him take DD1 to his friend's houses. Um..no.
The courts agreed with me, and told him he could see her at the social worker's office 2x a week until he got his life settled. Every week, twice a week, I would take her up to the sw office, and wait for 3 hours and he wouldn't show. For six months at a time, and then he'd show for one visit and get mad because she wanted nothing to do with him...she's 5 and she doesn't know who the heck you are!
I never bad mouthed him to her, and still don't to this day. She's asked, and I've answered, questions about his behavior towards her or myself, but only things that I can prove with documents from doctors/courts/etc. I tried everything to work with him, as I did DH (we got back together, and have a son as well---have been together for 21 years, less the year we were separated)...but he wanted nothing to do with it--it had to be his way or no way.
Anyways, some people aren't interested in being parents, they are just interested in hurting and inconvenicing the other party. Nothing you can do will fix that, so it's best to have the courts handle the issue, IMO>