If you decide to supplement vitD in winter time note that US government recommendations are way too low [1][2] compared to normal practices in Nordic countries: should be daily 3000 IU for kids (toddlers and up) and 8000 IU for adults.

[1] It's not sufficient for kids to take the bare minimum that avoids rickets. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3476526/)

[2] Statistical error in estimation of the recommended dietary allowance (RDA) for vitamin D (https://www.jpmph.org/journal/view.php?number=1915)