How do I bond with his son?

I've recently met my mans little boy (3 yrs old) and I find it hard to bond with. When around kids I feel like I freeze up as I have a fear of getting pregnant or having them. So I really don't know what I can do with him. He's lovely and loud and all I say is 'aww' and then look away. I feel very rude doing this but its because I have no idea what to do :(