My boyfriend and I are the biological parents of the youngest of 4 children in our poly family.
I don't prefer the term secondary-as he is a full-time member of our household and a full member of our family.
The youngest is 5. My oldest is 21. My husbands is 16. Our son is 12.
We're (obviously) poly and we're out-so all of the kids know and they all know whose bio-parents are who. But, they all call me mom and they all call Dh dad.
The baby calls bf by a special name, the other kids call him Uncle-because they did for years before we went poly.
"Love As Thou Wilt"