Julia Roberts celebrated her youngest son’s 17th birthday and took to Instagram to mark the milestone with a beautiful picture. Though the photo is rare, as Julia is typically known to be private about her kids, she and her husband have shown glimpses of Henry Moder before, which have left fans in awe. A hearty Happy Birthday is in order for the son of Hollywood couple Julia Roberts and Daniel Moder! Henry Moder, the youngest member of their family, turned 17 on June 18. His doting mom celebrated the joyous occasion with an adorable mother-son post, one of many that have prompted a flurry of p…