When painting figures (for example, from 1 to 10) it develops a color perception, fine motor skills, attention, diligence and accuracy, mathematical ability. Such tasks are connected to the process logic of painting, allow to fix the basic math skills or letters.
You should pick soft triquetrous pencils for a small kid. It is sufficient to have a set of six basic colors. When coloring, try pronouncing the name of each color, this helps the baby to remember them.