A 6 year old child who doesn't interact with other children of his age group and prefers playing alone in the same manner, is likely to be suffering from:-

C/F of Autism (marked impairment in reciprocal social and interpersonal interaction): Absent social smile. Lack of eye-to-eye-contact. Lack of awareness of others' existence or feelings; treats people as furniture. Lack of attachment to parents and absence of separation anxiety. No or abnormal social play; prefers solitary games. Marked impairment in making friends. Lack of imitative behavior. Absence of fear in presence of danger