Peter Robbins, the original voice of Charlie Brown in the Peanuts specials, did some "face acting" in the 60's as well. Here, he shows up in a season 2 episode of F-Troop.
In "The Sergeant & The Kid", Robbins is Joey Walker, a 10 year old left to be the man of the house after his father has died. His mother (Pippa Scott) isn't quite as thrilled about her son's dream of being in the Cavalry, so Sgt. O'Rourke (Forrest Tucker) and the gang have to try to convince Joey his place is at home.
I think the idea here was to at least tease a romantic interest for O'Rourke, to go along with the ongoing romantic subplot between Capt. Parmenter (Ken Berry) and Wrangler Jane (Melody Patterson). However, this ended up being a 1-shot.