I think it depends on how old the children are as to how much they need to know. I have always let mine pay for things in shops, so they knew from a very young age that you hand money over, get change, check it etc. My dad gives them pocket money each week and on a Friday they are allowed to take £1 to the corner shop to buy 'something you know you're allowed' ie not complete crap! My youngest is 6 and he can add up as he goes and always tries to work out his change before it flashes up on the till! You'd be surprised how many year 2 children don't even know the value of each coin, let alone have experience of handling real money.
When DH was made redundant without warning last year we didn't tell the kids to start with, but after a couple of months we did. I had to go back to work but to cut a long story short, I'm a TA and DH was in a global scientific sales field so I earn buttons compared to his earning potential. We have tried to keep life for the children as normal as possible, but they know money is tight and they're not to ask for 'stuff'. We have chosen to ensure they can still do their activities like swimming and brownies and so on, but all the extras like cinema, eating out and so on have stopped unless we have free tickets etc. we've tried not to worry them as that's not fair, but we've told them when we can't afford something, and they've been very respectful of that. They are 11, 9 and 6. Had they been younger we would have told them less to suit their age.
They all have a savings account for birthday/Xmas money and can use their money to buy whatever they like (within reason) but I have told them they have to leave £100 in the account , to try and encourage them to save, land start the idea of a savings pot which isn't touched.
They don't know about the child trust funds as we've never added to them, but I'm thinking that as DH gets a job (he's been out of work for 14 months now) and we have paid off the debt which is now building, that I might start adding to these do they have something as they get to 18. Not a fortune, but enough say for driving lessons or to build on for a house deposit. But I might change my mind by then!!!