Anyone's toddler been diagnosed with Vitamin D deficiency? What is the best supplement to give?

According to healthychildren.org page, Vitamin D is effeicient in making sure a baby or even an adult's body retains and absorbs essential nutrients such as calcium and posphorous which are both needed by the bones. A vitamin D deficiency can lead to rickets, a bone-softening disease that continues to be reported in the United States mostly in children in the first two years of life. In addition to vitamin supplements, enriched foods are another way to increase the vitamin D in your child’s diet. Look for foods fortified with vitamin D such as milk, cereal, orange juice, yogurt, and margarine. Source: https://www.healthychildren.org/English/healthy-living/nutrition/Pages/Vitamin-D-On-the-Double.aspx