It could be that. The maximum amount of child care expense that can be used for the credit is $3,000 for 1 child. If your flex plan paid $3,000, then you've already received the tax benefit on that amount and there's nothing left to use for the credit, even if you actually spent more than that. I say you received the benefit because the flex plan takes money out of your pay and puts it aside so you don't have to pay tax on it.
With 2 children, the maximum amount of expense that can be used for the credit is $6,000. So, there's some possibility that you could have paid $5,000 out of your flex plan and, if you actually spent more than $5,000, you could have $1,000 of expenses left to use for the credit.
One of the limiting factors for this credit is that it can only be taken until it reduces your tax owed to zero. If your tax owed is already zero, you get no credit.
