First, see the next question and answer.
However, most foods people eat are packaged and prepared, not basic fresh foods listed in the next question. The average grocery store has over 38,000 brand name food products as of 2010 according to the Food Marketing Institute. A complete list would be impossible here and I do not know if a lactose database exists. Also, food manufacturers change the formulas in their brand name foods and any list would soon become out of date. Lactose content is not required on the food label and food manufacturers are unlikely to analyze for nutrients not required by the Food & Drug Administration (FDA). Presently, you and your daycare will have to read food package label ingredient listing for milk, lactose, whey, curds, milk by-products, dry milk solids and non-fat milk powder. Foods that contain milk are required to be labeled as containing milk according to the 2004 FDA food allergen labeling regulations. So read food packages for “contains milk” tho do not rely on this food allergen statement alone without reading the ingredient listing.