From the start, typically developing infants are social beings. Early in life, they gaze at people, turn toward voices, grasp a finger, and even smile. In contrast, most autistic children prefer objects to faces and seem to have tremendous difficulty learning to engage in the give-and-take of everyday human interaction. Even in the first few months of life, many do not interact and will avoid eye contact, seeming indifferent to other people.

Autistic children often appear to prefer being alone rather than in the company of others, may resist attention or passively accept such things as hugs and cuddling without caring. Later, they seldom seek comfort or respond to parents' displays of anger or affection in a typical way. Research has suggested that although autistic children are attached to their parents, their expression of this attachment is unusual and difficult to interpret. Parents who looked forward to the joys of cuddling, teaching, and playing with their child may feel crushed by this lack of the expected and typical attachment behavior.

Autistic children categorically lack 'theory of mind', meaning that they are incapable of behavior cited as exclusive to higher primates such as adult gorillas, adult chimpanzees, adult bonobos and children above the age of five. Without the ability to interpret gestures and facial expressions, the social world may seem bewildering. To compound the problem, people on the autism spectrum have difficulty seeing things from another person's perspective. Typical 5-year-olds understand that other people have different knowledge, feelings, and intentions. An autistic person lacks this understanding, an inability that leaves them unable to predict or understand other people's actions.

Although not universal, it is common for autistic people to have difficulty regulating their behavior. This can take the form of "immature" behavior such as crying in class or verbal outbursts that seem inappropriate to those around them. The autistic individual might also be disruptive and physically aggressive at times, making social relationships still more difficult. They have a tendency to "lose control," particularly when they are in a strange or overwhelming environment, or when angry and frustrated. They may at times break things, attack others, or hurt themselves. In their frustration, some bang their heads, pull their hair, bite their arms, or even cut themselves.