Actually I believe that clip is from "A to Zzzzz"
Here's
Boyhood Daze, and Ralph in that is definitely the closest yet to what CP and I are remembering, particularly around the 0:48 mark. But not quite, unless we've both manufactured the same false memory.
It may very well have been just one-off incidental character, some infant in a stroller or the like. Younger than Ralph is portrayed. And more rudimentary in style, one of those where you could practically still see the pencil marks.