I have copied this information from a website.
The following list is what a four year old should be able to do:
Knows names of familiar animals
Can use at least four prepositions or can demonstrate his understanding of their meaning when given commands
Names common objects in picture books or magazines
Knows one or more colors
Can repeat 4 digits when they are given slowly
Can usually repeat words of four syllables
Demonstrates understanding of over and under
Has most vowels and diphthongs and the consonants p, b, m, w, n well established
Often indulges in make-believe
Extensive verbalization as he carries out activities
Understands such concepts as longer, larger, when a contrast is presented
Readily follows simple commands even thought the stimulus objects are not in sight
Much repetition of words, phrases, syllables, and even sounds