The purpose of using rods, cubes, or tally marks in teaching numbers is to provide concrete representations of abstract numerical concepts. They make numbers less abstract. Numbers are abstract ideas. Using physical objects like rods, cubes, or tally marks allows children to see, touch, and manipulate quantities, making the concept of a number more tangible and understandable. This is a primary goal of using manipulatives. The other options are either incorrect or describe a specific function rather than the overarching purpose. While children do count cubes and rods, and tally marks can aid in skip counting, the fundamental reason for using these tools is to bridge the gap between concrete experience and abstract mathematical understanding. The most accurate statement is that they make numbers less abstract. The final answer is $\boxed{\text{They make numbers less abstract.}}$