I have 2 kids under 10, and both my husband and I work full time and have some (non-relationship) activities outside of the house, so finding relationship time can be challenging. I don't think I could have managed poly when the kids were under 5 unless with someone I worked with. I was just too tired!
I manage it now, but not at all in the form that I initially expected, and the adjusting of expectations along the way was not always easy. Both my life and my boyfriend's are very home-centric; it is simply expected that kids/families will take priority and get the bulk of time. He and I manage to carve out a few hours each week, though. We have a pretty reliable routine for meeting after work. It's mostly just talking time - not that much by way of formal activities or intimate time. It has been frustrating at times to have such limited opportunities to share some of the normal aspects of life, but we value what we do have, and we're very close emotionally. Its very unusual for him; he's been far more prone to flings that end when the NRE wears off.
The anarchy idea is useful here - it's much easier to simply enjoy what we have if it's not always being judged against a particular model and found wanting.