Though children see colors when they are much younger than 3 years old, at the age of 3 they begin to differentiate between them. This includes both being able to tell the difference between colors visually, as well as being able to verbally name them.
By 3 years old, a child should be able to learn to count up to the number 10 and, in some cases, beyond. Counting individual objects is also a milestone development at this age. Grouping or sorting sets of items by number is another developmental step, though it may come after counting.
Children at the age of 3 should know approximately 500 and be able to use them in simple sentences. Communication of emotions, wants and needs are also a learned skill, and should be encouraged by the parent for both mental and emotional development. Standard 3-year-old verbal development also includes properly learning to use plural nouns and simple verb forms, such as the past tense.
Learning to distinguish one thing from another is a big part of learning as a 3-year-old child, and it is an important step in mental development. Most children pick up the ability to tell differences without much coercion, which is a sign that they are thinking logically and of their own free will.
Three-year-old children have a difficult time of learning the differences between small increments of time, such as seconds, hours and minutes. Time is most easily learned when applied to actual events in a child's daily life. For example, explaining that a child needs to go to bed at 7 p.m. or eat dinner at 5 p.m. gives her a concrete concept of when a time is and what she should do. Learning days is as simple as explaining the days you are off of work or when you have a family outing.