Perhaps not for the household, but children (and teens) spend a great deal of their allowance money on junk foods via vending machines and the corner store as well as pestering their parents to distraction to buy them the latest and greatest "treat" they just saw on a commercial watching TV.
Without getting into an off-topic discussion about who should be making the dietary decisions for the family, I know a lot of parents who pretty much let their kids pick whatever they want in their lunch box. Guess what their kids are choosing?