Throughout their second year, children become more skilled with their hands. This includes being able to hold crayons and scribble with them using increasingly complex movements. Although they are able to do more and more as they develop, it is difficult for most two- to three-year-olds to draw within the lines of a coloring book.
Fentress, J. C., & McLeod, P. J. (1986). Motor patterns in development. In Blass, E. M. (Ed.) Handbook of behavioral neurobiology, 8. Developmental psychology and developmental neurobiology. New York: Plenum.