[hiimshort]

It's a harmless bit. The joke (if I remember correctly) is that these two creatures are aliens that pop up and don't know what the thing in front of them is. For children (and adults) it is silly because, of course, we know what a computer is – we've seen one dozens of hundreds of times! Compound that confusion with a silly way of speaking to reaffirm that they're not from earth and it makes you giggle.

As for the developmental impact, I think it's quite positive. Sesame Street has been and continues to be a great source of knowledge and useful lessons & morals for children. Adding in some silly situations like this helps keep them engaged and develop their sense of humor.