Box 10 is dependent care benefits, either on-site day care provided by the employer or a dependent care FSA. You must run the dependent care credit interview to tell the program how to treat this money. You will be asked how much you used (how much reimbursement you got) and how much you forfeited (left in the account unused). You will also be asked about child care that you paid for your dependents. If you used the money for qualifying child care, or forfeited the money, it is not added to your income. But if you withdrew the money but used it for non-qualifying care expenses, the amount is added back to your taxable income.
If you did not have a dependent care FSA or on site day care, your W-2 may be incorrect and you need to get a corrected one from your employer.