My son, who s now 5, and my daughter, 6, have both attended births before. And yes I think because he does not have vigina, he will grab his penis. My son has done the same thing. It passed. I think mostley because I told him that women give birth, and as a boy what he can do, is hold hands, help get med. stuff, so now he does have a doll, who is the same size, and he holds her hands and tells her everything is ok. Some times he will yell at me to get water. But that is how we got him from touching himself and the labor thing. It might have passed on it own, who knows.
But my son started being at births at age 2. At age five I have no worries that he might be affaid of anything later in life. I figure if he sees it as normal, and no one is freaked out about it, he will grow up more in touch with reality about babies, sex, and womens bodies.