OMG, K.! What a kook your husband's co-worker is!
I am a California-licensed cosmetologist. One of the most enlightening things my professors taught me was that cutting, shaving, etc. the hair has ZERO effect over future hair growth. (Not talking about cutting off damaged ends to prevent future breakage, of course...we're talking about future growth from the source). By shaving/cutting on the hair surface, you do not effect the hair papilla, rooted within the epidermis/dermis....where all the "action" is. They blew away the ever-so-popular old-wives-tales about not shaving your legs or the hair will grow back thicker and darker. This is simply an old belief that is scientifically proven wrong, yet so many still choose to believe it. (Have you ever seen women who have never shaved their legs before? They have thicker, darker hairy legs than they did when they were a child!!!)
Anyhow, back to your little man's dome....Even if you shaved your little guy bald (a common practice in the Hindu religion at 1-year, and, trust me, there hair grows back just beautifully), you would not effect the future growth of his hair.
So, trim away, and make your little guy look all handsome, and ignore that silly co-worker....who probably would've told you when you were pregnant that if you had heartburn, you were going to have a hairy baby! Oy ve!!! LOL