By 3 years....

These are the milestones I'm currently looking for in my 2 and 1/2 year old, by 3 years most children will:
-ask alot of questions (you will know when a child has reached this milestone, they ask questions all day long about everything! Kayden got here a few months ago and he asks questions from the moment he wakes up until he goes to bed. My mouth is sometimes ready for a nap by 8am because I'm constantly responding to him!)
-match primary colors and might name a few (Kayden has known his colors for awhile now. But many of my preschoolers I work with do not. It isn't a big deal but something to work on and watch for)
-understand some time concepts (for example "tomorrow we are going to the park" and they understand when that is, etc. some other early time concepts are yesterday, after, before, next week)
-usually have a vocabulary of 800-1000 words
-know their full name, sex, and part of their address
-know the difference between boys and girls
-frequently talks to themself
-can tell a story
-uses at least 3-4 word sentences
-can sing songs and recite some nursery rhymes. (nursery rhymes are important to teach, they have rhymes in them which is great for emergent literacy and they teach the flow of language in a fun way)
-can use all the different sentence types (statements, questions and commands)
-repeat sounds, words and phrases
-tell you when they need to go to the restroom
-like to whisper
-can deliver a simple message (for example you tell them- "tell daddy you are going to the park" and they go and tell daddy the message)
-are about 80% intelligible to a stranger
-can pay attention to an activity or book for about 20 minutes

milestones taken from Speech Language Hearing, Development in Preschoolers