Standard deduction impacts when not claiming child as a dependent

When filing the return for my dependent child, TurboTax reduces the standard deduction from $12,000 to $350 plus the earned income amount if earned income is less than $700, and also reduces the tax due if the dependent is not claimed on another's return. I haven't been able to trace the calculation backup for the reduced tax amount.  Can someone steer me in the right direction?