'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.<br />
