How can I tell if my infant son is gay?

You can't tell if your son is gay simply because he is interested in things that some gay men, and nearly all babies, would be interested in. And childhood won't give you an accurate picture, either. As children, my sister and I both loved trucks, fighting, getting dirty, and had no female friends. We're both heteroual. I think you may be looking at this just a tad (emphasis on tad) too closely. Just enjoy your son.