Clinical Efficacy and Long Term Effects of Transcranial Direct Current Stimulation (tDCS) in Children With Attention Deficit/Hyperactivity Disorder (ADHD)

* Children, male or females presenting a sufficient compliance for participate aged 7-14 years at the time of Visit 1 (Enrolment/baseline). * Children's parent or legally authorised representative must sign informed consent. The children must sign assent if applicable (depending of age and understanding). The principal investigator of the center where the child is included signs the document, certifying that the family and the child, or their authorised representative, have received informed consents. * Children meet DSM-5 criteria for ADHD (combined presentation) based on a clinical evaluation using questionnaire ADHD-Rating-Scale (ADHD-RS) and the Kiddie Schedule for Affective Disorders and Schizophrenia French version (Kiddie-SADS). * Subjects have a minimum ADHD-RS total score of 32 at Visit 1. * Children have a minimum CGI of 4 at Visit 1. * Children have an age-appropriate intellectual level evaluated with WISC-5 (Full IQ \>80). * Children in which stimulant medication have been tested previously and stopped for adverse effects could be included in the study after a wash out of at least seven days. Exclusion Criteria: * Children have a neurological pathology or handicap: Epilepsy, cerebral palsy, sequelae of brain injury (traumatic or ischemic or inflammatory...) * Children have a comorbid psychiatric disorder: conduct disorders, autism, severe obsessive-compulsive disorder, mood disorder, bipolar illness, conduct disorder, psychosis, and substance abuse. * Children under medication (stimulant or other psychotropic treatment, benzodiazepine, antidepressant, hypnotics and melatonin) or who did not respond previously to stimulant will not be included. * Severe sleep disorder. * Contraindication to tDCS.