Well, we always used to insist that the kids got nothing as in terms of treats bought by us weekly, had a basic pocket money of £5.00 for everything they wanted but earned money by doing things to be helpful. As sherrard says some things were expected anyway, but main things like bathing the dog, weeding, doing all the laundry etc gained additional money, so that by the time they were 8-10 they were pretty savvy with money, knowing they had to manage it carefully and that their own efforts lead to nicer things. By 11 their allowance went up to incorporate enough to buy clothes shoes etc once they'd got the hang of it, and we allowed them to be entirely self managing with regards to that.
Don't feel under pressure to do things you don't feel you can financially, give them what you can afford and tell them the financial situation, kids are very grown up given the opportunity to be, and it won't hurt them any.