My parents separated when I was 7. My parents had a voluntary agreement wrt money but I don't think my dad ever really stuck to it. He used to give my mum money in front of us and it looked very generous (£100 or £200 at a time) but I worked out pretty quickly that that was only 2 or 4 supermarket shops and therefore was a bit pathetic.
My mum never mentioned a lack of money. We didn't get everything we wanted, far from it, but she never cited lack of money as the reason. She just said no and that was the end of it. It was only when I was an adult that I truly appreciated how difficult it must have been for her financially, brought home by her having someone remove some built-in cupboards she'd hated for over 20 years - she simply hadn't had the money to do it until we all left home.
Didn't feel that mum had been dishonest as this was only one of a huge range of things she didn't discuss with us!
Find it much more difficult to work out now that I am in a similar situation. Quite frankly, I find my lack of income (we are living on my part-time earnings alone) scary and the DCs have, not surprisingly, picked up on that. I then find myself overcompensating to try to convince the DCs that financially everything is okay and there is nothing to worry about (I feel very strongly that they are too young to have to have adult worries, they're coping with quite enough as it is).
My DD misses nothing and has already made a rather derogatory comment about dad not paying for things. I said 'well dad isn't working at the moment'. I want her to know she can moan about her dad to me, that I will sympathise but that I won't collude or criticise him. Obviously, there are times when it's very very hard not to say 'Yes, I know he's ......' but know it's not in her best interests.