They work together but the FSA is generally better. You can use the FSA for up to $5000 of care expenses. The credit can be used for up to $3000 of qualifying expenses for one child or $6000 of qualifying expenses for 2 or more children. So if you provided care for 1 child and had an FSA for $4000, you can't apply anything to the credit (you already applied more than $3000 to a benefit). If you have a $5000 FSA and provided care for 2 children, you can apply $1000 to the credit.
