I think a small part of it is the work of children, but many, many, people just don't know and even more just don't care. I work in a grocery store and the other day a woman noticed a log cabin on the reverse of a penny. I explained to her that it was the first of a series of four reverses from last year, honoring Lincoln's 200th birthday. She had no idea. Also this week a young guy and his dad (who is in his 40's) brought me a 1909s VDB penny. "We looked it up on the Internet and we think it's worth quite a bit." I told them no. It was 3 inches in diameter.
When old aunt Martha passes away and her nieces and nephews get together to clean out the house for the auction, all those little tubs and trays of coins are taken to a bank and cashed in for some green stuff. If the teller handling it doesn't notice or care (and most don't) all those coins go into the pot.