That needs good coordination even in mom-dad situation. And gets more and more complicated if more people are involved.
More specifically for polyamorous, it seems to keep much harder a stable, jealousy-free, neutral relationship. Even in mom-dad, kids tend to pick favourite parent or parent picks a favourite kid and that creates all sorts of issues. This would definitely add much more tension with multiple "moms" and "dads" around.
Don't they always adapt to different rule sets anyway? There is one set at home, one at school, one when they go visit the grand parents and one for whoever is babysitting. There is a lot of overlap but a lot of exceptions/infractions depending on the context. Plus kids are more or less constantly probing for edge cases and try to push the boundaries naturally.
