Why does everyone say "see if he is open to having other kids" when there's clearly another option: You can have kids with another man if he doesn't want to. Unless you identify as monogamous, i.e. you are only able to love one person at a time, then maybe you'll meet someone else down the road that you'll want to move in with and have kids with.
It's not wrong at all if you don't want to share your partner. But obviously, it does mean that this is not the partner for you.
One thing to note, if he's poly, he's far less likely cheat or leave you for another woman.
I don't need labels to define me. They're sticky and I hate the glue they leave behind.