• Limited reciprocal sharing of sounds, smiles, or facial expressions

• Does not respond to gestures and facial expressions used by others
• Limited or no eye contact
• Limited response to their name being called
• Does not spontaneously use gestures such as waving, reaching, or pointing while interacting with others
• Diminished, atypical, or no babbling

Age 9-12 months

• Lacks interest in toys, or plays with them in seemingly unusual ways (e.g. lining them up, spinning, smelling, opening/closing parts rather than using the toy as a whole)

• Emerging repetitive behaviours (e.g. flapping hands, rocking, spinning)

Age 12-18 months

• No single words

• Doesn't point to show others things they're interested in
• Lack of pretend play
• Limited joint attention (initiating, responding, sharing of interests)

Age 15-24 months

• Diminished, atypical, or no spontaneous or meaningful two-word phrases

Anytime during the early developmental period (6 months – 36 months)

• Loss of previously acquired language or social and communication skills
• Repeats words or phrases over and over (echolalia)
• Gives unrelated answers to questions
• More interested in looking at objects than other people's faces
• May be content to spend extended periods of time alone
• Seems to be in their "own world"
• Avoids or ignores other children when they approach or interact
• Has trouble understanding other people’s feelings or talking about their own feelings
• Displays a strong reaction to certain textures, sounds, or lights (e.g. may reject clothing or want to be completely covered, puts hands over ears, stares at lights)
• May appear indifferent to pain or temperature
• Insists on routines (e.g. has to perform activities in a special way or certain sequence, requires a particular route) and is difficult to calm if even small changes occur
• Preoccupation with unexpected interests, such as light switches, doors, fans, or wheels, and difficult to distract from these activities 
• Uncommon fears, but may not seek comfort from adults