Britney Spears' sons are growing up so fast!The pop superstar took to Instagram over the weekend to send sweet birthday wishes to her sons: Sean Preston, who turns 15 on Monday, and Jayden James, who celebrates his 14th birthday on Saturday.«My two lil men’s birthdays are this week !!!!!!» Spears captioned an artistic photo which shows two flowers blooming from a cloud in a red night sky . «You guys are getting older and so big and are waaay cooler than me!!! I love you both to the moon and back