For me, it is a no-brainer. If he is a good man and you are attracted to him in a way that you could see yourself with him, then God will give you every grace for strength and generosity of heart to accept the children as well. And I'm sure you will be blessed in ways you would never have dreamed, and all the fear of the unknown dissipated.
I just witnessed a similar situation of one our AMS members on one of our retreats. There was a man there who told us about a woman he was considering marrying. The woman had eight children and that concerned him. But he said that the retreat helped him be totally resolved that she was the one, and that he was going home to ask her to marry him. For him (as could be the case for you), there was a tremendous opportunity to have a family that otherwise he was not likely to have (due to them both being in their 40s).
So if you have love to give and faith to share, why not consider the eight children as well? I know that is a tough concept to digest right away (having an "instant" family), but someone has to love that man in marriage, and someone has to be the mother of those children. Why not you? I have seven children of my own and I can really imagine what this man you are seeing must be going through when he considers any woman who might be interested in him. He is probably a little concerned that the women will be scared off by the number of children he has. And many probably are. But for some reason, you are not. And that is a sign to you (and to him) that this could be "doable".