How much can children earn before paying tax?

Answer 1

It depends on the source of the income (self-employment, wages, unreported tips, etc.), the total income for the year from all sources, and whether someone else (like their parents) can claim them as dependents.

See Tables 1, 2, and 3 on pages 2, 3, 4 of Publication 501 for the federal rules:

http://www.irs.gov/pub/irs-pdf/p501.pdf

State rules are different for every state. The minimum income can be much higher or much lower than the federal minimums. Refer to the instructions that come with your state tax forms or the web site of your state tax department for details.