Is this world's strongest six-year-old?

If you think Arat Hosseini is just another six-year-old, think twice. The Instagram star, soccer prodigy and expert gymnast has wowed the likes of Lionel Messi and Cristiano Ronaldo, as well as Tennis great Novak Djokovic.

Hosseini, who is of Iranian origin, has become an Internet sensation because of his training routines and...