Ragnar Thorson, age 5

Ragnar Thorson has a hereditary condition that's rare in humans. As he grows up, his muscles will (slowly at first) automatically begin to resemble those of an obsessed body builder -- complete with abnormally low body fat. Due to another hereditary condition, he has abnormally dense bones.

He had "six-pack abs" before he was even potty-trained.

As a toddler, he was slightly anemic due to having insufficient bone marrow. Moreover, he sinks in fresh water. Most people can float.

As a toddler, his electromagnetic powers began "leaking." However, his memories start at age 5 due to amnesia. At age 7, he goes on the run because his forgotten past begins catching up to him.