1 to 2 Years: The Scribbling Stage
Most twos are in the random-scribbling stage of making their mark in the world. They take great pleasure in feeling the movement of their arm and the crayon. They often don't ever look at the page as they create! Eventually they become aware of the cause and effect of their movements, and the resulting drawings. Two-year-olds may start to label or name their scribbles.
3 to 4 Years: The Pre-Symbolism Stage
Many threes are in the controlled-scribbling stage. Their improved motor control and eye-hand coordination allows them to explore and manipulate materials with a more purposeful action. Children at this stage enjoy the result of repeating similar actions, of creating shapes such as circles, spirals, and lines. By age 4, they may have expanded their shape repertoire to include ovals, squares, rectangles, as well as wiggly and jagged lines. At this stage, their work is more purposeful. They are attempting to represent the human form with simple figures that consist mostly of heads with legs and arms. As children explore basic circles and lines at this stage, they also start experimenting with simple shapes that represent letters to them. They may also make a few familiar letters repeatedly and "read" them to you.
5 to 6 Years: The Symbolism Stage
By age 5, children start experimenting with simple representational drawings. Favorite subjects include self-portraits, their family, house, pets, vehicles, and nature. At this stage some children will begin to include more detail in their drawings. Now their figures have clothing and expressions and can be placed in a setting that has a "ground" at the bottom of the page. Fives and sixes have more control over the direction and size of the lines they draw, and pay attention to where they place them. Their art reflects their personality and relationships. They use art to communicate feelings and ideas. As their drawing becomes more representational, their writing becomes more recognizably letter based.
For more information, read Ellen Booth Church's "Learning From Children's Art and Writing."