From the article:
In adjusted models, paternal vitamin D intake was positively and statistically associated with offspring’s height and weight at 5 years old; whilst these associations were reduced, and no longer statistically significant, when offspring reached 9 years old.
[…]
Skin exposure to sunlight is essential for the body to produce vitamin D, so the authors also looked at the number of hours children aged 5 spent playing outdoors during summer. They found that spending 3 or more hours playing outdoors during weekends was related to increased height at 5 years of age.