You must have an approved Disability Tax Credit Certificate on file with the Canada Revenue Agency in order to claim the caregiver amount for your child. Please see the following link for more information, https://www.canada.ca/en/revenue-agency/services/tax/individuals/topics/about-your-tax-return/tax-return/completing-a-tax-return/deductions-credits-expenses/canada-caregiver-amount.html#documents.