Depending on the order you entered things, one of two things probably happened:
1) If you entered the W2 first, then entering the Box 10 amount will increase your taxes until you go through the child care section and add the info about your qualifying child care expenses. Dependent Care Benefits (DCB) are taxable if not used for qualified child care expenses, so until you've entered those expenses TurboTax will treat the DCB as taxable.
2) If you entered the child care expenses first before entering and DCB from box 10 of a W2, then TurboTax would have calculated the child and dependent care credit (typically 20% of child care expenses). When you later entered the DCB from box 10, that reduces your eligibility for the care credit. (Because you're already not paying tax on the DCB, you don't get to take a credit on those same expenses.)
Either order you use, it's going to look like your taxes went up as the result of the DCB, but once complete info is entered you'll have an accurate result.
