Most people pour their cereal into a bowl first and then add the milk. Then is done so that the milk completely covers the cereal. However, there may be times when you may not be eating the bowl of cereal for a few minutes. If this is the case, then you may want to pour in the cereal last after the milk because this will keep the cereal from getting mushy from the milk. It will keep the cereal crisper.
Therefore, determining when you should add the milk depends on when you plan on eating the cereal. It also depends on the type of cereal that you will be having. Cereals that break apart more easily wil get mushy sooner.
Cereal should be put into the bowl first because if you pour the milk in first, the cereal gets too soggy. When you pour milk into the bowl, you have a very limited amount of time to eat it before this occurs.
Also, putting the cereal into the bowl first ensures that the milk to cereal ratio is balanced correctly and the milk tends to stay fresher when you pour it in after the cereal. The best part of eating cereal is the fact that it is crunchy at first, and then once you get to the bottom, you get to drink the milk.