I'll start with a question... Is the 63K before or after taxes?
The short answer to your question on how much is reasonable is: "It depends." It depends on a lot more than where you live, it depends on what you want... do you want to pay down debt? Do you want to save? Are you trying to buy a house? Those will influence how much you "can" (should let yourselves) spend. It also depends on your actual salary... just because I spend 5% of my salary on something doesn't mean bonkers to you if you're making 63,000 and I'm only making 10,000.
I also have a lot of respect for you trying to take this on. It's never easy. But I would also recommend you start by trying to see what you can do to track how much you are actually spending. That can be hard, especially if you mostly use cash.
Once you're tracking what you spend, I still think you're coming at this a bit backwards though... rather than ask 'how much is reasonable' to spend on those other expenses, you basically need to rule out the bigger items first. This means things like taxes, your housing, food, transportation, and kid-related expenses. (I've got 2.5 kids of my own.)
I would guess that you're listing your pre-tax salaries on here... so start first with whatever it costs you to pay taxes. I'm a US citizen living in Berlin, haven't filed UK taxes, but uktaxcalculators.co.uk says that on 63,000 a year with 3 deductions your net earnings will actually be 43,500. That's 3,625/month.
Then what does it cost you each month for rent/utilities/etc. to put a house over your family's head? The rule of thumb they taught in my home-economics class was 35-40%, but that's not for Europe... you'll know what it costs. Let's say its 1,450 a month (40%) for rent and utilities and maybe insurance. That leaves 2,175.
The next necessity after housing is food. My current food budget is about 5-6% of my after-tax salary. But that may not compare... the cost to feed a family of 3 is a fairly fixed number, and our salaries aren't the same. As I said, I am a US expat living in Berlin, so I looked at this cost of living calculator, and it looks like groceries are about 7-10% higher there around Cardiff than here in Germany. Still, I spend about 120 € per week on food. That has a fair margin in it for splurging on ice cream and a couple brewskies. It feeds me (I'm almost 2m and about 100 kilos) and my family of four. Let's say you spend 100£ a week on groceries. For budgeting, that's 433£ a month. (52 weeks / 12 months == 4.333 weeks/month) But let's call it 500£.
That leaves 1,675.
From here, you'll have to figure out the details of where your own money is going--that's why I said you should really start tracking your expenses somehow... even just for a short time. But for the purposes of completing the answers to your questions, the next step is to look at saving before you try spending anything else. A nice target is to aim for 10% of your after-tax pay going into a savings account... this is apart from any other investments. Let's say you do that, you'll be putting away 363£ per month. That leaves 1,300£.
As far as other expenses... you need some money for transport. You haven't mentioned car(s) but let's say you're spending another 500£ there. That would be about enough to cover one with the petrol you need to get around town. That leaves 800£
As far as a clothing budget and entertainment, I usually match my grocery budget with what I call "mad money". That's basically money that goes towards other stuff that I would love to categorize, but that my wife gets annoyed with my efforts to drill into on a regular basis. That's another 500£, which leaves 300£.
You mentioned debts... assuming that's a credit card at around 20% interest, you probably pay 133£ a month just in interest... (20% = 0.20 / 12 = 0.01667 x 8,000 = 133) plus some nominal payment towards principal. So let's call it 175£.
That leaves you with 125£ of wiggle room, assuming I have even caught all of your expenses. And depending on how they're timed, you are probably feeling a serious squeeze in between paychecks.
I recognize that you're asking specific questions, but I think that just based on the questions you need a bit more careful backing into the budget. And you REALLY need to track what you're spending for the time being, until you can say... right, we usually spend about this much on X... how can we cut it out?
From there the basics of getting your financial house in order are splattered across the interwebs. Make a budget... stick to it... pay down debts... save. Develop goals and mini incentives/rewards as a way to make sure your change your psyche about following a budget.