Four-year-olds have an increased capacity for learning math concepts. They use logical reasoning to solve everyday problems, and can effectively use language to compare and describe objects and shapes. They can count to "ten," recognize written numerals "0" to "9," and add and subtract using numbers up to "four." Four-year-olds know some variations of a circle, square, triangle and rectangle. They know days of the week, months, and the seasons, but still cannot tell time.
http://www.pbs.org/parents/childdevelopmenttracker/four/mathematics.html