"He Ain't Heavy, He's My Brother" by the Hollies. Cute note - when our two boys were very young (age 4 and 2), the younger one was rather pudgy (he's thin as a rail now). But invariably people would pick him up and say something like "Whoa - aren't you the heavy one?". We taught the older one to pipe up and reply "He's not heavy, he's my brother". Couldn't bring myself to teach him the bad grammar so we took poetic license with it.