'You are loved and I believe in you': Jennifer Garner posts heartwarming letter her five-year-old son Samuel put in a library book.br br Leaving letters in books is a long-standing tradition.br And Jennifer Garner and Ben Affleck's five-year-old son Samuel has clearly cottoned on to the custom quite early in life.br On Monday Jennifer, 45, showed her Instagram following a heartwarming note reading: 'Hello, You Are LOVED. I BeLieve in you,' that Samuel put in a library book.br br The little tyke signed off with a lopsided heart.br br 'When the librarian finds a love note your son tucked into a picture book...,' Jennifer wrote proudly in her Instagram post's caption.