Say Hello by Michael and Jack Foreman

From chapters.ca:
A lone dog comes upon a group of kids playing ball and with leaping ease, joins the game. They’re all having so much fun, they don’t see a sad little boy standing off by himself. Who will spy the boy and invite him to play? With arresting images by a master illustrator and a simple, touching text by his son, Say Hello evokes the joy and relief of finding a new friend just when it’s needed the most.