According to Canada Revenue Agency (CRA), your child may be eligible for the Disability Tax Credit when a medical practitioner certifies, on Form T2201, Disability Tax Credit Certificate, that the child has a severe and prolonged impairment in physical or mental functions, and the CRA approves the form.

To get the Child Disability Benefit (CDB):

• You must be eligible for the Canada child benefit (CCB)
  
• Your child must be eligible for the disability tax credit (DTC)

If you are already getting the CCB for your child who is eligible for the DTC, you do not need to apply for the CDB. You will get it automatically.

For more information, please see CRA webpage: Child Disability Benefit (CDB)

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