My Great Big Momma by Oliver Ka, illustrated by Luc Melonson

From chapters.ca:
Size matters, according to this groundbreaking picture book - and in a good way. Here, a young boy describes his large mother in caring terms - her softness, her warmth, how comfortable and reassuring it is to sit on her lap on the bus. But when she goes on a diet "because of what people say," he becomes a picky eater himself to show her how foolish she's being. This remarkable book offers a charming and timely picture of a special relationship between a loving mother and the little boy who understands that people should be appreciated for who they are.