Early MathVenn diagrams, numbers to 100
Write each number in the diagram. If it fits no circle, write it outside.
A Venn diagram is a good way to see what a common multiple is. These free printable worksheets sort eight numbers to 100 by two multiplication tables, and whatever lands in the overlap belongs to both. Answer key included.

The answer key prints on a separate page.
With multiples of 4 and multiples of 5, the number 28 goes in the first circle alone and 55 goes in the second circle alone. 40 and 80 belong in the overlap because they are in both tables, and the idea of a common multiple is now something a child can point at. 57 and 79 are in neither table and stay outside the circles.
The checking is the real practice here. A child who is sure of the tables can place a number at a glance, and one who is not has to divide, which is useful division practice with a reason behind it. When a pair such as 2 and 3 comes up, the overlap fills with multiples of 6, and that pattern is worth pointing out.