Drinking milk to have loose bowels is generally caused by allergies to milk. After this happens, you can take the following measures to deal with it:

First, don't drink milk first, you can give your child some warm water, which is helpful for conditioning.

Second, you can take your child to the hospital for allergen testing, and you can determine what kind of substances your child is allergic to by doing this test. Third, see if the milk has expired.