Helpful advice from James Dobson: (via Bradford Plumer)
[T]he boy's father has to do his part. He needs to mirror and affirm his son's maleness. He can play rough-and-tumble games with his son, in ways that are decidedly different from the games he would play with a little girl. He can help his son learn to throw and catch a ball. He can teach him to pound a square wooden peg into a square hole in a pegboard. He can even take his son with him into the shower, where the boy cannot help but notice that Dad has a penis, just like his, only bigger.