Be a chef. At concerning eleven years old, I used to sell meals to my brothers (I had four of them). I got 25 cents for tangled eggs or a sandwich, and more for more multifaceted meals. My brothers chosen to stay in facade of the TV and let me cook for them. Since the food was by now provided by my parents, the proceeds was pure profit.
Computer whiz-kid service. Many young kids know a lot concerning computers. My nephew was getting paid for indoctrination by the time he was fourteen, but even younger kids can demonstrate old folks how to use a computer and the internet for a fee. Learn a few more skills, and they can even set up computers for new owner who are using them for the first time. Letting grandparents increase the word would be a good marketing ploy.
Family carnival I charged my brothers 5 cents for a wad up piece of paper selected from a bucket full of them. Most had a penny or two within them, but a few had a quarter. It was just one of my "carnival" events. I also had those throw pennies at a bowl across the room that I kept, of course. If a penny stays in the bowl they won a dime. I am almost painful to say how much of their well-deserved paper route money I took from them.
Collect returnable we collected and return cans and bottles for a deposit as kids. Now that more states have return laws, it's an even better way to create a little cash. During the Cherry Festival, when I lived in Traverse City, Michigan, adults come to town just to collect the cans that people throw all over. With a 10 cent deposit, they were collecting more than dollar 100 worth per day according to quite a few of them. If the kids wear gloves, leave broken down cans and bottles alone, and use hand sanitizer, this is a safe way to make money.