My boyfriend is a Rat and I am a Pig. I have three children, (15,10 and 9), but he doesn't have any.

Hey, you are a wonderful pair and the love will last long. But for kid matter, you'd better discuss with him in advance. Tell him about your thought of unwilling to have more children. If he accepts this, do stay together with him. If he wants his own kid, would you make a compromise? You should understand him.