In a piece called "As Boys Get Fatter, Parents Worry One Body Part Is Too Small," Dr. Perri Klass assured parents not to freak out if the baby's member seems rather hidden.
"Questions about penis size have become more common over the past decade, as my colleagues and I have all seen more overweight children coming in for physical exams," she wrote.
While most of the penises that doctors see are of normal, proportional size, there is a phenomenon called the "hidden penis" that effects kids who are overweight:
The penis can be buried in the fat pad that sits in front of the pubic bone, and it can remain hidden as boys go through adolescence. What is called a “hidden penis” can be a combination of being prepubertal (so the penis has not begun to grow), being overweight (so the fat pad is significant), and in some cases an anatomical condition in which the soft tissue below the skin of the penis doesn’t adhere well to the Buck’s fascia, the thick covering that surrounds the penile nerves and arteries. This fixation problem can yield what Dr. [Aseem] Shukla described as a “slidey” penis, in which the actual shaft retreats and only the skin, or the foreskin, in an uncircumcised boy, is clearly apparent.
That's right, "slidey penis" is a medical term, and there are some surgical procedures that exist to excavate a concealed penis. Dr Aseem Shukla says that such surgery is only for extreme cases, and that the "hidden penises" tend to reveal themselves after children grow to be older, and ideally, slimmer.
So don't worry, Mom and Dad. Odds are, your son's penis is alright, and things will even out with some weight loss and a whole lot of puberty.
Pediatricians often both assure both the parents and the kid that they're growing up normally. Dr. Shukla had some pretty poignant advice in the Times for people with genitalia that don't grow up in nudist colonies:
“I basically say, first of all I want you to know that you are absolutely and completely normal,” Dr. Shukla said. “We don’t all walk around with our pants down, and we don’t see how everybody is. But you should realize the private area can be different, and because yours looks different from your brother’s doesn’t mean there is something wrong.”
Everyone's private parts are different, and because we have minimal points of comparison, it's easy to assume the worst.
But penises, like people, are all different and special in their own way.