The Fair Labor Standards Act restricts the types of jobs and the hours a child under the age of 16 is allowed to perform. Most counties don't even allow children to get working papers until they are 14 years of age. That just means that 12 year olds need to become a little more creative when it comes to ideas for making extra money. The jobs must also be easy to perform since a 12 year old still has a lot of growing up to do.
Deliver newspapers or flyers for local businesses. A 12 year old can easily ride a bike to deliver newspapers on a paper route. He could also go around and ask any local businesses if they have any flyers they need passed out.
Put up signs for a mother's helper in grocery stores, or pass out flyers in a daycare. You could make money playing with the mother's children while the mother cooks dinner. You may also be asked to help with a few of the household chores. This is an easy way for a 12 year old to make a few extra dollars.
Make a snack mix and sell it to other kids in the neighborhood. You can make the snack mix any way that you want, so it is easy to do. Just throw a combination of popcorn, pretzels, corn chips, mini marshmallows, chocolate chips, or Chex cereal together. Separate it into individual plastic zipper bags and sell them on the school bus or at your school's sports games.
Become a dog walker or a pet sitter. Many pet owners don't have time to take their dogs for a long walk so they look to hire someone else to do it. Also, if your parents approve, you could offer to do some pet sitting jobs. For example, the next time the owner of a hamster or gerbil goes on vacation, you can stop by once a day to take care of it, earning some easy money.
Start your own lawn care business. You can easily mow lawns in the summer, rake leaves in the fall, and shovel snow in the winter. You may want to charge an hourly wage instead of saying $10 per lawn. Some lawns are larger than others so an hourly wage is more fair. All you have to do is hand out flyers to get a few customers. Those customers may then recommend you to others if you do a good job.