My child qualifies for the Disability Tax Credit so I should be able to claim an addt'l $500 for the Children's arts tax credit. However, the program maxes out at $500.

Did you answer yes to the question asking if there was an accepted T2201 at CRA?

Yes.  DTC checked and applied.  I checked the deductions summary page and saw an amount of $1000 for the arts amount.  Like the others have said, it automatically applied the extra $500 even though the deductions page showed you are only allowed $500.  Thank you.