Britney Spears is celebrating her son Jayden James Federline’s 20th birthday with a sweet — and candid — social media post. “Happy birthday to my handsome young boy oh dear lord we have this beautiful thing called life in front of us, it’s such a beautiful delicate thing,” the pop star, 44, wrote via Instagram on Saturday, September 12, alongside a vintage-looking photo of Jayden. In the pic, Spears’ son can be seen wearing a flannel buttoned shirt and a pair of black pants while posing for an unidentified photographer. “I hope I can be the best mommy in the world every day...