If things get serious and he lets you into that part of his life, then great!
You can get to know his child and have outings and do fun things together.
You will never fully get to experience or enjoy your relationship if there’s always a third party stirring the pot.
It is also important to set boundaries with him involving his child.
He was still a person, and I would feel bad if I didn’t give him a chance just because he had a kid. However, I learned there was another child later on, an infant only six months old.