I understand your frustration OP.
I was in the same situation as you a few months ago. Although I don't have any kids, I was working in a minimum wage job. I'm under 25 as well which meant I only got £7.70 an hour. I had to work 40-50hrs a week in order to earn a decent wage (well not even a decent wage but enough to cover rent and bills) and I was probably left with around £100 a month afterwards which was for gas, electric, food and petrol. There was no way I could squeeze in luxuries such as a holiday or new clothes.
I appreciate money/luxuries aren't everything, but when you work your ass off 40hrs a week and are left with hardly anything after paying all the bills it can become quite depressing.
I live on my own, pay for everything by myself. As I have no children I don't receive any help and I'm not entitled to working tax credits as I'm under 25. There was a period where I was off work for around two months last year due to a family bereavement and I received £500 monthly from UC. I received less because again, I was under 25. This was suppose to cover my rent, council tax, water rates, gas, electric, car payment, petrol and food. My rent is £450 a month so my monthly payment covered that and that was it. Luckily my mum was able to help me get through it and pay the rest of the bills, but if she hadn't I would of well and truly been screwed.
Having experienced these two situations, I can see both sides of the coin. But I do believe some people "work" the system in their favour. You will find most people on Mumsnet don't want to believe their is actually people who do this, such as parents claiming to be single when that is just not the case. I know a single mum who does this and gets around the same amount in benefits as what I earned working full time in my previous job, so whether people choose to believe it or not, it does happen.
I don't have any problem with people getting what they are entitled to, it's the greedy pricks who lie through their teeth to get more that pisses me off. It's not as if people in work can do that. I wouldn't be able to work 40hrs and then say to my employer I worked 50 in order to get more money. The system should monitor these types of people more closely imo.
I also don't agree with pp who say "if your not happy in your current job then get a better one". If everyone felt that way and decided to leave and retrain, then who would do these jobs. We still need care workers, nursery workers, cleaners etc. Minimum wage should be scrapped and changed to the living wage at £10 an hour. People shouldn’t receive less just because their under 25 either.
I'm extremely lucky that I'm no longer in this position and have been in my new job for around 5 months now, which pays a fairly decent wage (Above minimum wage) and I now have disposable income after I've paid all my rent and bills, which hasn't been the case for many years now. It's nice to be able to spend my money on days out and a few little luxuries now and again, it makes going to work worthwhile.
I do hope your situation improves OP as sadly I can’t see any of these issues being addressed any time soon.