erika: Get a job. You would need to find a restaurant that would be OK with hiring a kid for less than minimum wage. Unless you're old enough to get a job. You can also deliver newspaper at a very young age. You can make stuff and sell it on your parents ebay account. You can buy stuff at yard sales for cheap and resell them online for more money.
Most other ways to make money as a kid are illegal but you can look on wikihow. They have things about how kids can make money and how people can make money. Look through both of them and see what they say
"A kid" isn't specific enough, but if you're at least 14 (13 some areas) you can become a soccer referee and do a few games on weekends. Clubs always want young kids to start.
Walk dogs. Baby sit. Clean people's garages. Pull people's weeds out of gardens. Use your imagination..if you see a fence needs painting knock on the door and offer to do the work.