"His leg was slightly bow legged, but it kept bending, it kept getting more and more bow legged," said Justice's mother, Robin Grubb.
So she brought him to Boston Children's Hospital, where Justice's x-ray gave doctors a diagnosis.
Curved, translucent bones re an indication of rickets - an old-fashioned disease caused by a severe vitamin D deficiency.
"When you heard the word rickets, were you flabbergasted," said Robin Grubb. "I'd never heard it before."
Doctors thought they'd eradicated rickets a century ago. But now it's making a comeback - as are other bone density disorders.
"It's a public health problem, really a hidden epidemic," said Dr. Catherine Gordon.
Amazingly, the sun is a big part of the problem - nobody wants to stand in the sun and sunlight is a major source of vitamin D. After years of being told to avoid direct sunlight, and to slather on plenty of sunscreen, dermatologists have convinced us sunshine can be deadly.
"There is no reason to risk cancer by going out in the sun more. You get enough sun through casual exposure when you walk to the car or run errands," said Dr. Darrell Rigel, a dermatologist.
Dr. Catherine Gordon countered: "We get into lively debates with dermatologists and I think there's a very minimal but a critical amount of sunshine that we all need to get each day."
She prescribes as little as five to 10 minutes, saying that will provide two to four times the recommended daily amount of vitamin D for fair-skinned people. African-Americans may need a bit more. And in the winter, people living in the sun-deprived northern latitudes may need to take a vitamin D supplement.
Robin Grubb said that since she's seen rickets close up, she's serving more meals rich in vitamin D and she's re-thought her attitude about covering up Justice. Now, she says, her family no longer runs from the sun.