There is great variability in pattern recognition and drawing among children.
Pattern recognition tasks can involve stimuli of varying degrees of concretness, complexity, and motivational value for the child. Other variables include the past experiences of the child, and the mode of response employed (eg. Pointing, drawing, etc.)
Let me give a general, if not relatively meaningless, rule of thumb, that a child should be able to recognize and draw a Cross by the age of 2, a Circle by the age of 3, a Square by the age of 4 and a Triangle by the age of 5 years of age. Note, however. the picture to the right (in the graphic vesion) drawn by a 3.5 year old girl.
This includes circles, rectangles and oblique lines (which you wouldn't expect until 5 yrs.)