What to do?

I need advice.  Harrison is 20months.  He's in the 4th percentile for weight.  Douglas was the same at that age.  Travis probably is too.  :-)  Anyway, I'm having trouble with him eating all of a sudden.  He used to (before his throw up bug in Feb) eat super well (and still only 4th percentile).  He ate fruit, veggies, and generally anything you put in front of him.  Now he sucks.  Seriously.  He won't eat the fruit he used to.  He won't eat bagels, oatmeal, or other breakfast food he used to.  He is stubborn too.  With Douglas I could have said at 20months, eat it or go hungry and he would have eaten it.  Harrison has been sitting at the table for 1 hour with his breakfast in front of him.  I don't know what to do.  Do I let him sit there some more or get him down and he can't eat anything until snack time?  At snack time do I try to get him to eat his breakfast again?  That will result in more tears and I don't think he'll eat it.  Or b/c of his low percentile for weight, do I just offer him anything he will eat?  Douglas was the same weight and Travis is itty bitty too so I kind of think I shouldn't cater to him.  AHHHHHH!!!  What do I do?