Box 10 is for the dependent care FSA contributions for the year. Unless you have childcare expenses during the year that qualify to offset the amount, then it becomes taxable income.
If you used the money to pay for Dependent Care Benefits, then during the W-2 interview process, on the pages that follow entering the actual boxes, you need to answer "Yes" to used money to pay for dependent care expenses.
Then, you will need to go through the Dependent Care section under Deductions and Credits. When it asks again if you used the money for dependent care for the year, you answer "Yes".
