There are a couple of issues that may affect you. If you are paid more than $2000 (in 2016) for the year, you may be considered an employee. If you are an independent contractor, that does not apply. The difference can be complex and you should seek personal assistance.
If you are an independent contractor, you need to claim all your income as self employment income. In addition, if you make more than $400 (from all sources), you will have to pay self employment taxes. That's a bit over 15%. (This is probably the limit you were looking for).
Those paying you can claim up to $6000 a year in Dependent Care Credit, if their children meet the age and other requirements.
