(Since when does Ernie say "Hi-ho"?)
The little boy in this clip is named Jason Kingsley, and he is the son of Sesame Street writer Emily Perl Kingsley. I don't know how noticeable it is in the video, but he has Down syndrome, and when he was born in 1974, the doctors told his parents that he would never be able to function at even the most basic cognitive or affective levels, and that they should have him institutionalized immediately...and then go home and tell their friends and family that the baby had died.
Wow. I mean, the recommendation for institutionalization was, regrettably, pretty standard at that time1...but then to lie about it? That's harsh.
Fortunately, the Kingsleys didn't take the doctors' recommendation but instead took a social worker's advice about an early intervention program that involved lots of physical and mental stimulation. And what do you know, they found out that kids like Jason can learn if people around them make the effort to try to teach them. Moreover, by having Jason appear on Sesame Street, they had the opportunity to show the world that the doctors had been wrong in saying that he'd never be able to sit or stand or walk or talk or read or write or have a sense of humor,2 etc.
Now, in the interest of full disclosure, I must admit--with shame--that my track record for compassion for the developmentally disabled is sketchy at best, and it's something that I continue to struggle with to this day. However, I can personally attest to the fact that seeing people with Down syndrome (etc.) on television can be a powerful teaching tool in that regard. In fact, though it would probably be impossible to prove one way or the other, sometimes I wonder what effect Sesame Street had on the passage of the Americans with Disabilities Act in 1990.
1To make matters worse, for a long time those institutions were little more than prisons, although I don't remember the timeline for when the reforms occurred and the situation may have improved by the '70s.
2There's a really charming clip, which unfortunately I am unable to find online, with Ernie and Jason, in which Ernie is holding a mirror and says, "When I look into the mirror, I see me, Ernie!" Immediately, Jason turns the mirror around and says, in mock exasperation, "No, no, no, no! I see ME, Jason!" It continues on that way for a while, with Jim Henson barely able to contain his giggles, until finally they decide to look into the mirror together. But it goes to show that not only did Jason talk and have a sense of humor as a little boy (and presumably still does), but he had genre savvy and a sense of comedic timing as well.