The child is under age 18 and has a physical impairment or a mental function disability. The child's condition significantly limits him or her in carrying out his or her life habits compared with what is expected for a child his or her age. The expected duration of the disabilities must be for at least one year.

https://www.retraitequebec.gouv.qc.ca/en/forms/forms-concerning-family-allowance/forms-handicapped-children/reassessment-report-various-medical-conditions-eligibility-supplement-handicapped-children/application-supplement-handicapped-children