No, your son does not have to be living with you to make the claim.
"If the DTC is not required by the person with a disability to reduce their taxable income to zero, then it may be transferred in whole or in part to a family member who supplied some or all of the basic necessities of life such as food, shelter and clothing to the person. Even if the person with the disability is not living with you, you may still be able to claim the DTC if the person depends on you for regular and consistent support for one or more of the basic necessities of life such as food, shelter or clothing. You may be asked to provide receipts or other documents to support this claim".
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