Just gonna add a ditto. Kids are self-absorbed, they care about how adults treat them, not about the nuances of the connections between those adults that don't pertain to them. I've read a number of accounts of kids raised in poly families, and it doesn't seem to bother them, with the exception of parents who start doing poly when their kids are teens and have already formed their values, in which case I've heard of a story or two where a kid was very offended and judgmental. Its like kids raised by gay parents. It may not be the norm to the rest of society, but to them it's normal, versus if you come out as gay to them when they're mostly grown, you can't necessarily predict their reaction.
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.