What made you suspect your child had diabetes?

I have a 4 yr old who is CONSTANTLY hungry.  He wakes up sometimes at 0530 - 0600hrs and heads straight to the fridge or pantry to eat.  He'll eat 4 yogurts and a muffin before I get up at 0700 hrs and make him breakfast which he eats in full.  I realize he is growing but this has been fairly constant for a couple years now.  He often disappears to sneak food!  I don't keep a lot of junk food around (he'd inhale it!) so he makes fairly healthy choices (pears, cheese, yogurt) eating anything that he can easily open, so I don't worry too much but I have a nagging feeling something is going on with him (tapeworm maybe?). His height and weight are totally normal but his is a bit on the hyperactive side. I don't restrict his intake (as long as it is a healthy choice) but I do get tired of him thinking I'm a walking concession stand!  He rummages thru my purse looking for a snack and is miserable if he can't find something!!  He always has water with him and drinks adequate amounts daily.  His older brother could go all day without asking for food.  Just really wondering what symptoms brought you or you doctor to test for diabetes?  Thanks