Dog and baby.

I have a rescue that got when he was 4 months old. He will be 7 this year. I'm now pregnant and very concerned   He doesn't seem to like little kids in his home. He snapped at my niece and charged her. He also growels at other little kids. I couldn't imagine giving him away. Does anyone have suggestions on what I can do to make him like kids? At the park or pet smart he is great with kids. It's just at home.