Sean is the son of Lennon and Yoko Ono. He also has a brother, Julian, who is the son of Lennon and the late singer's ex-wife Cynthia Lennon. James is McCartney's fourth kid under his first marriage with Linda McCartney, who died in 1998. James has four other sisters.
Lennon has been on a Beatles' kids photo tour of sorts. Last week, he snapped a picture with George Harrison's son, Dhani, leaving fans to wonder if there's more to come -- or hope for a reincarnation of the iconic boy band.
"Now you guys get Dhani and Zack in the new band! Beatles the Next Generation!" said one commenter.