Please help me understand child tax credits v. vouchers from work

[sleeplessbunny]

I've recently separated and have 2 DC, 4 and 2. I work 30hrs and never thought I'd be entitled to any benefits but looked at the calculator on a website last week and found I could actually claim child tax credits to the tune of around 3k/yr. I have got the forms now and am about to fill them in, but before I do I'd like to know:
a. I currently use a vouchers from work to pay for a lot of the childcare (but they don't cover it all). I get the impression I can't do this once I'm claiming CTC. Is that correct? Can I keep claiming the vouchers until my CTC come through and then cancel them? Or do I have to cancel them before I apply?
b. When my 2yo starts school my childcare costs will go down and I suppose my CTC will reduce or stop. Could I restart the workplace vouchers then?
TIA

[sleeplessbunny]

Anyone? The more I look at the rules online the more confused I am getting...

[ilovenavy]

You can't claim them at the same time, no. I didn't realise and had to pay the money back.

If I'm correct in thinking you cannot claim for childcare credits until you have spent all your childcare vouchers.