Billy and Bobby Bittles

Billy and Bobby are twins just like the Tibble Twins that made their first appearance in the episode So Long, Spanky.

Just like the Tibble Twins these two twins are trouble makers, like to annoy D.W., and possibly everyone else in the class at the preschool.

They even tried putting a spider on D.W. only for the spider to be eaten by the toad that was hiding in D.W.'s backpack, which caused the twins to flee in fear.

It's revealed in the episode So Long, Spanky that Billy is a vegetarian. Other than that not much is known about them and they have yet to be mentioned and have never appeared since that episode.

It's likely they were intended to replace the Tibble Twins, but apparently the plan never happened and were subsequently regulated to minor characters throughout the remainder of Season 1.

Despite this, they appeared again in the episode Arthur's Almost Live Not Real Music Festival as part of the chorus that was singing the Library Card Song.

Billy also appeared in the episode Arthur's Lost Library Book, where he was in the library with D.W., Edwin, and Unknown Female Aardvark while Mr. Ratburn did a puppet show for them.

These two characters have since completely disappeared from the series altogether after Season 1 and their last hurrah was the episode Arthur's Almost Live Not Real Music Festival. They have not been mentioned or seen since.

Appearance
Billy and Bobby are both bears with a light gray complexion. Billy wears a purple shirt with a single yellow stripe, short tanned khakis, cream colored socks, and brown shoes.

Bobby wears a green shirt, blue overalls over his green shirt, cream colored socks, and brown shoes. Both twins have some hair on their heads.

Trivia

 * Even though these two characters no longer appear, it's very possible that they have been "reincarnated" into Liam and Unknown Male Bear.