Molly’s Family by Nancy Garden, illustrated by Sharon Wooding

From chapters.ca:
The members of Ms. Marston's kindergarten class are cleaning and decorating their room for the upcoming Open School Night. Molly and Tommy work on drawing pictures to put on the walls. Molly draws her family: Mommy, Mama Lu, and her puppy, Sam. But when Tommy looks at her picture, he tells her it's not of a family. "You can't have a mommy and a mama," he says. Molly doesn't know what to think; no one else in her class has two mothers. She isn't sure she wants her picture to be on the wall for Open School Night. Molly's dilemma, sensitively explored in words and art, shows readers that even if a family is different from others, it can still be happy, loving, and "real".