If your child is six months old, you should consider talking to your doctor if your child exhibits the following behavior:

•  Doesn't reach for things
•  Show no affection for caregivers
•  Doesn't respond to sounds around her/him
•  Doesn't make vowel sounds (eh, ah, oh)
•  Doesn't laugh or squeal
•  Seems unusually stiff or unusually floppy

If your child is nine months old, you should consider talking to your doctor if your child exhibits the following behavior:

•  Doesn't look where you point
•  Doesn't respond to his/her own name
•  Doesn't babble (mama, dada)
•  Doesn't play back and forth type games
•  Doesn't seem to recognize familiar people

If your child is one year old, You should consider talking to your doctor if your child exhibits the following behavior:

•  Doesn't point to things
•  Doesn't learn gestures like waving bye bye, or shaking head yes or no
•  Doesn't search for things that she sees you hide
•  Doesn't say single words like mama, dada, up, bye, this, that, juice
•  Doesn't crawl
•  Loses skills he/she once had

If your child is 18 months old, you should consider talking to your doctor if your child exhibits the following behavior:

•  Doesn't point to show things to others
•  Doesn't know what familiar things (cup, spoon, phone) are used for
•  Doesn't imitate or copy others
•  Doesn't have at least six words
•  Doesn't gain new words
•  Doesn't notice or react when a caregiver leaves or returns
•  Doesn't walk
•  Loses skills he/she once had

If your child is 2 years, you should consider talking to your doctor if your child exhibits the following behavior:

•  Doesn't use 2-word phrases (mama up, want milk)
•  Doesn't know what familiar things (cup, spoon, phone) are used for
•  Doesn't imitate actions and words
•  Doesn't follow simple instructions
•  Doesn't walk steadily
•  Loses skills he/she once had

If your child is 3 years old, you should consider talking to your doctor if your child exhibits the following behavior:

•  Has unclear speech or drools a lot
•  Doesn't speak in sentences
•  Doesn't follow simple instructions
•  Can't work simple toys (simple puzzles, turning knobs/handles, peg board)
•  Shows little interest in toys
•  Doesn't want to play with other children
•  Doesn't play make believe or pretend
•  Doesn't make eye contact
•  Falls down often or has trouble on stairs
•  Loses skills he/she once had

If your child is 4 years old, you should consider talking to your doctor if your child exhibits the following behavior:

•  Ignores other children
•  Doesn't respond to people outside the family
•  Shows no interest in make believe or pretending games
•  Can't retell a favorite story
•  Doesn't follow 3-step directions
•  Doesn't use "you" and "me" correctly
•  Doesn't understand "same" and "different"
•  Speaks unclearly
•  Doesn't scribble or has trouble scribbling with a crayon
•  Loses skills he/she once had

If your child is 5 years old, you should consider talking to your doctor if your child exhibits the following behavior:

•  Doesn't show a wide range of emotions
•  Shows behavioral extremes (unusually aggressive, fearful, sad, shy)
•  Is unusually withdrawn and not active in social situations
•  Is easily distracted and has trouble focusing on an activity for more than five minutes
•  Doesn't respond to people or responds only superficially
•  Can't tell the difference between real and make believe
•  Doesn't participate in a wide variety of games and activities
•  Can't give his/her first and last name
•  Doesn't use plurals, pronouns or past tense properly
•  Doesn't talk about daily activities
•  Doesn't draw pictures
•  Loses skills he/she once had