Sell your soul to the devil
Babysit, then with the oldest group you babysit, offer to run a lemonade stand with em. Do most of the work, but have THEM sell it. Parents and adults love little kid lemonade stands. Be nearby so they know your supervising them. Do this on especially hot, clear days for max profit. Split the end profit with the kids by maybe 30-45%. Their cut has to be larger or they'll lose interest. Either way, if you sell $100 worth of lemonade, you just made an extra $30-45. And that's on top of babysitting, for roughly $10-50 depending on the family.
Or you could babysit an entire group of kids from multiple families and make like ~$60 a day. Make lunch, sit em in front of a TV, then take them outside to run around and go batstuff, then theyll wanna take a nap.
Any teenagers, p. much let em do whatever. Anyone below 11 is pretty much under your command.