These "expenses" are considered the normal cost of raising a child (in Canada). You cannot deduct any such expenses, unless, for example, you had to pay for child care to allow you to work. The person you paid would declare those payments as income and provide you with a receipt for income tax purposes. Generally, only one party can claim a child as a dependent and be entitled to the related deductions (e.g., the deduction for a dependent). This is usually the party with whom the child is deemed to have their principle residence. Since you are the one paying child support, it would be unlikely you would qualify for these deductions. Income tax returns for separated parents are routinely checked to ensure that both parties have not claimed deductions that only one of them is entitled to make. While I was paying child support, I was contacted two or three times and asked to provide additional information over the phone or to send them additional documentation. They even called me once to get the new phone number and address for my ex-wife, as she had moved and they were auditing her tax statements. They do check up on you.

Child support is not a deductible expense, neither is other expenses spent on your children. Only Alimony is tax deductible to the payer and taxable to the receiver.