In Easy Step mode the Nova Scotia Children's Sports and Arts Credit is under Deductions > Claim Dependant Credits (in the left side menu ≡). If you are using Forms mode in TurboTax CD/Download it’s on the bottom half of the Dependant pop-up screen.

it seems they will not allow expenses for a second child if they do not have a SIN, even though it is not required by CRA

Did you add the child without the SIN as a dependant? If yes, please try to enter 000 000 000.

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