Obviously Cereal, THEN Milk. Would you put the dressing in, then the salad? No! If you are putting less Milk than Cereal purely by volume, then, if you pour the Milk over the Cereal you guarantee better liquidy coverage of the Cereal! IT IS SCIENCE!
Cereal - Milk. If it ever differs in my presence you may be killed. Same goes for those people that bite ice cream off the cone, I will call the police. Stop it!
Sometimes if my kids are really hungry, they put cereal, then milk... then eat up all the cereal, and add more cereal to the milk. So they kind of do both.
Me, I'm cereal first... when I eat cereal (which is rare). Usually I toast my homemade bread and put peanut butter or Nutella on it. So much tastier....