Experimental: PACT + Management as usual

PACT + management (MAU - see comparator intervention). PACT is a parent-mediated and video-aided intervention designed to improve socio-communicative functioning in children with ASD. The intervention is based on theory and research on pre-linguistic and early social interaction and language development. The programme focuses on changing the interaction in the parent-child dyad in order to enhance communication and language development and skills in children with ASD.~The overall focus of the intervention is to guide parents to provide a sensitive, highly adapted interaction context in which their own responses and language are matched to the child's communication competence and language comprehension. Parents learn to identify windows of opportunity to facilitate joint interactions, enhance emerging communication, elicit child intentionality and support language comprehension, thereby aiming to ameliorate abnormal developmental pathways.

Active_comparator: Management as usual

Enhanced management as usual (MAU). MAU is delivered by the regional Child and Adolescent Mental Health Center (CAMHS). All participants will have equal access to seek advice via a telephone hotline in the trial period (12 months).~Following the diagnosis of ASD, the parents will be offered psychoeducation as usual in the local CAMHS. A telephone hotline open to all participants will offer pedagogical advice and try to help the parents to collaborate and engage with their professional partners in the municipality. The parents will also be able to contact the CAMHS when needed. The hotline team will be able to consult with the responsible clinician at the CAMHS. The clinician should always be notified within the same day, if a parent describes acute worsening of the child's condition, risk of suicidality, or severe aggression. The responsible clinician will be able to refer the child to further assessment and treatment within the CAMHS without any significant delay.