William Li is Wanda's younger brother. He is kind of mischievous. While he can walk and somewhat talk, he's being potty trained, sleeps in a crib, and drinks from a bottle. He appears in "Ups and Downs", "Under Construction" and "Meets Molly Cule" (in Wanda's fantasy).
William has straight black hair similar to his sister. He's most commonly seen wearing a red T-shirt and blue shorts.
In the new series, William wears a yellow T-shirt, blue overalls and white and blue sneakers.
- "Ups and Downs" (first appearance)
- "Under Construction"
- "Meets Molly Cule" (in a fantasy)
- "The Magnetic Mambo"
- "The Tales Glaciers Tell" (cameo)
- Lisa Yamanaka also voiced William along with his big sister Wanda.
- He is aged up in the third series.
- He is even more aged up in the new series.