Im suposed to get a refund but i can`t prove my income?

Of course. The IRS has no reason not to believe you. Try to reconstruct the income you received. In a calendar agenda try to do it by date. Each time you believe you babysat, put down the approximate hours and the time, from when to when. At least you have something to show the IRS if you get audited. The refund is yours, don't lose it for lack of responsibility on the part of the people who hired you.