Childminders Club: Childcare Tax Credits

I have just agreed to take on 3 month old baby for 4 days pw but the couple (dad in work and mum at uni) have not yet applied for Child Tax Credits, she will need me to put my registration number on her form that she is sending off which she is bringing round this week. I am a bit concerned as I always ask for payment in advance (1 month) but couple said they were applying for CTC - do both parents have to be working to receive it? are they likely to get 70% of childcare as mum at uni? I know it is not supposed to be my worry but I am just trying to decided whether to insist on payment up front (in which case I may lose the placement) or to go with it and hope for the best....