Having taught math to young kids, I used cubes at the beginning to give a real feel to the numbers. Having tangible items to play with gave them a real world demonstration of how numbers work.

And when the kids grasped the physical manipulation, I would transition to paper exercises like you are looking at. And I would call those squares "cubes." because doing so linked the physical with the abstract. And for some students, to suddenly switch terms could be confusing at first.

Teaching is about linking back to things the student already knows and is comfortable with.