This Oscar-winning animation was adapted from Dr. Seuss's story by Phil Eastman and Bill Scott, directed by Robert Cannon, and produced by John Hubley. I remember watching the Gerald McBoing-Boing cartoon series as well.
They say it all started
when Gerald was two—That’s the age kids start talking—least, most of them do.
Well, when he started talking,
you know what he said?He didn’t talk words—he went boing boing instead!
Via Boing Boing