How did the little boy in Dear Frankie know his real dad died?

Answer 1

In 'Dear Frankie,' Frankie knows his father is dying because his mother tells him that his dad is really sick. He drew a picture for her to give to his father in the hospital. She finds out later that Frankie knew the man she had paid to pretend to be his father, really wasn't his dad, and that his real dad has passed away, when she reads one of his letters to his 'fake Dad.'