Those are Pectoral Muscles, Son
Our two year old is still nursing, partly because I've completely forgotten how to wean (if I ever knew how in the first place) and partly because he is just so darn cute when he asks to nurse. Our other children were weaned between 20 months and 2 years, but I don't recall any of them being as obsessive about getting their RDA of mama's milk as Baby Wingnut is.
The main problem now is that he is constantly talking about everyone's "two nursies." Having older siblings is often an even bigger problem, because they think this stuff is hilarious and have now taught Baby Wingnut other ways of referring to "nursies". The latest incarnations are nipples (pronounced very funnily as "whipples") and "I have two man b**bs!"(pronounced very clearly). The latter one got an immediate nix from Wingnut, who insisted the kids teach Baby Wingnut, "I have two Pecks!"
Calgon, take me away!