The title is from an English nursery rhyme: "Three little kittens had lost their mittens..."
This is the only appearance Clint Howard, brother to Ron Howard, makes in this series. But while he had not yet reached his seventh birthday when this episode originally aired, his acting career at this time in his life was already quite a busy one. By the time he appears here, he had already appeared in multiple TV shows and at least one movie. In a little more than a year from playing Ralphie here, he would star in his own TV show: Gentle Ben (1967).
This is Richard Champagnie's only credited appearance in the series. Two days after this episode originally aired, he would make his third of 16 appearances on the TV sitcom Gomer Pyle: USMC (1964). He's, of course, best known for his recurring role as Father Mulcahy on M*A*S*H (1972).