My tax return is asking for the dollar amount on my son's tax return from form BC428. However, when I go to my son's return there is NOTHING about this form there.

When you go through the Provincial section of your son's return, at the end it will show a summary that includes the amount of British Columbia non-refundable tax credits. 

Or, you can you can look at the PDF archive of your son's return to see the BC428 form.