Vitamin D deficiency is established as <20 ng/mL in adults. So far, there is no established level for infants and children; however, most providers use the adult standard. Some providers go even further and consider all levels <30 ng/mL to define deficiency in children.
Schnapps is a type of distilled spirit that has two meanings. Essentially, schnapps are made by fermenting the fruit along with the base liquor (usually brandy), whereas liqueurs are often made by steeping fruits in alcohol after fermentation and/or distillation.
Much higher in alcohol (107 proof / 53.5% Alcohol by Volume) the brand GoldschlÃ¤ger is a cinnamon schnapps which also has gold flakes in it. It is available in most US major metropolitan markets. Either brand will suffice, though I prefer Danziger Goldwasser because it's only 40% Alcohol by Volume and easier to drink.