Snappy Larry's Showtime (partially found Nick Jr. interstitial series and American dub; mid-2000s)
Snappy Larry's Showtime was a British interstitial series that was aired on Nick Jr. around the mid 2000's.
The premise of the series is like so: Snappy Larry would introduce the show and explain the sing-along feature. He would introduce an animal who would then sing a nursery rhyme with sing-along lyrics at the bottom of the screen. After he/she finishes singing, Snappy Larry wraps up the show.
An anonymous user on Answers.com recalls an episode that features the song "London Bridge", but did not specify the animal who sings it. YouTubeFan43 recalls an episode where a yellow snake sings "Pop Goes the Weasel". Recently, a full episode featuring a lion singing "Looby Loo" was found. Before this, a short clip from another episode was surfaced.