I don't go to church, so take it with a grain of salt, but I'd be annoyed, too. I don't see why they need to have 3 separate treats in 2 hours? Also, why why why would you feed kids a junk food snack before lunch? Or any snack? What is the point of that, can the director explain her reasoning at all?
I'd probably tell the children's ministry director that you would prefer they give them the heatlhier snack during Sunday School at 10 and then skip the snack during Children's Church. If they have a healthier snack early on, the chances are greater that they'll be able to last until lunchtime. With a cookie and candy earlier on, they're dealing with a roomful of kids on a sugar crash.