Im going to be babysitting, and giving receipts. I was going to claim the income from it.. What would I be roughly looking at paying back??

You are self employed. You must file your tax return if yourself employed income is $400 or more. You will report your income and expenses on schedule C or C-EZ (Form 1040). This income is subject to SE tax at 15.3%. Read: Your U.S. Tax Return: Tax Filing by Self Employed Sole Proprietor or Independent Contractor