Zero is the Leaves on the Tree by Betsy Franco, illustrated by Shino Arihara

From chapters.ca:
It's easy to count three of something - just add them up. But how do you count zero, a number that is best defined by what it's not? This important math concept is beautifully explored in a way that will inspire children to find zero everywhere - from the branches of a tree by day to the vast, starry sky by night.