It helps to have both a current and former partner who step up and do their bit when it comes to the kids. I don't have to chase them. They organise their working lives so they are available to parent. Plus,our other partners often see us in parent mode (they both get on with our kids and are significant in their lives) so we aren't having to step away from parenting to have a bit of time with our other partners. Of course we do have time away from them too.
Then, because we all understand the importance of quality adult time, we go out of our way to consider each other. My partner's girlfriend will volunteer for babysitting when she knows our anniversary is close so we can get a hotel for the night. We'll catsit for her and her wife so going away for a week or more is a possibility for them. I babysit for my exes kid (he has has a child with his current partner) and he has both of mine (our child plus my child with my current partner) either for childcare purposes or just to give each other a break.We're a united network and we get that the more adults there are pitching in, the fuller life we can lead as parents.
Broadly speaking,there is "kitchen table" polyamory which looks a lot like what I do and there is parallel polyamory where there is less integration between all the members. For us, people seeking kitchen table polyamory (where everyone can comfortably have dinner together and wants to be able to do that) are most compatible. If you're happy to interact with my kids and other partner(s), there are no real limits to how far our relationship can go. If you prefer parallel polyamory, the chances of us bonding enough to be more than casual lovers is slim.