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).
- "Ups and Downs" (first appearance)
- "Under Construction"
- "Meets Molly Cule" (in a fantasy)
- "The Magnetic Mambo"
- Lisa Yamanaka also voiced William along with his big sister Wanda.
- He is aged up in the third series.