To present a different viewpoint for consideration: I do not see what exactly is wrong with a baby, under two, wanting the comfort and closeness of skin to skin contact with his Momma. This is absolutely normal and what is wrong is the way U.S. "culture" has decided that any form of touch, or any needs of a baby must be somehow "wrong".
Infants have needs. One of them is to be very close and to be cuddled as they are falling to sleep. Ours is the only society in the world where we believe somehow that babies should be willing and happy to sleep alone in a room away from their families-and that they need "discipline" if they express a need for closeness.
It is far more "inconvenient" and troublesome to deal with the lifelong insecurities and emotional stiltedness that comes from not having one's real, developmentally directed needs met when one is young.
When my little ones were this age, I thought it was the sweetest thing in the world that they would put their little hands on my breast/chest as they snuggled to sleep. It was a sign that they knew they were loved and all was right with the world for them. They are now all very self-assured, reliable, mature (more than their "age level"), capable and confident at age 18, 14, and 9.
This is not "groping" as one person here said--that happens with men who are not able to figure out why they are still obsessed with breasts (perhaps they didn't get enough touch as babies?), not with little babies who can't even talk yet.
Leaving a baby to "cry it out" when he is expressing himself the only way he knows only leads to insecurities and the sense that he is imprisoned. Instead, give the snuggles and the holding that the baby needs now, and watch how, over the coming few years, he develops into a self-assured, confident boy who knows he is loved and expresses love to others.