Jack Osbourne marked his 36th birthday.MORE: Sharon Osbourne surprises fans with romantic wedding photoIn honor of the happy occasion, his proud mom Sharon took to Instagram to share a throwback photo of her youngest child - and he looks so different.WATCH: Sharon Osbourne’s kitchen inside her $12million mansion is like an American dinerThe image sees Jack as a toddler, holding his teddy bear and sitting next to his rock star father Ozzy.