The benefits of a FSA account is to reduce your taxable income. However, you're allowed to claim child care expenses in your tax reporting at the end of the year. I guess you'd have to see if the reduction in taxable salary is more beneficial to you than claiming the deduction during tax season. (i.e. Does the reduction knock your taxable salary to a lower tax bracket?) Another thing to note - if you don't use it - YOU LOSE IT. No refunds of unused money in your FSA.
Basically, you calculate what it would cost you on an annual basis for child care, divide that by the number of pay checks you receive and have that number deducted from your check each pay period. With my account, I would have to pay the child care provider up front as I usually do, submit a claim and wait for a reimbursement check.
I personally found it a pain to constantly submit claim forms, wait for reimbursement and essentially struggle with the child care cost being taken out of my monthly budget twice until the refund check came in. I did that all last year (2008) and this year (2009), I'll just take the deduction at tax season.
My 2 cents - hope it helps.