Get your taxes done using TurboTax

If you all live together :   although you could make FSA contributions they are considered unused and will simply be added back to your wages on the tax return so you will only escape FICA taxes on the contributions.   It would be better if the parent claiming the child employ an FSA account. 

Now if you do not live together ... the custodial parent can get HOH filing status, the EIC and the form 2441 even if the non custodial parent claims the dependent and the CTC.