Okay OP - compare and contrast.
I'm in the central belt of Scotland, quite a nice little historic town that's considered the more...upmarket town in my area. It has direct transport links to both Glasgow and Edinburgh and there is lots to do round about to keep you entertained. It is very cheap living.
The beautiful cottage that I rent (lounge, kitchen/diner, bathroom, study/TV room, two double bedrooms, driveway for 2 cars, spacious patio garden and garage) would set you back between £450-500 per month. Gas and Electric is around £80 a month (we pay a little more each month just to make sure we stay in credit). Council tax/water and sewage is £100. After that, it's just your added extras such as broadband, mobile contract, etc. Top end total for a warm roof over your head with the rates thrown in: £700 per month.
Childcare here. For an all day placement at a nursery for an under 3 you're looking at around £30-35 a day. School based nurseries take from either 2 or 3 years for 5 mornings/afternoons a week and they are of course free places, for those who want their child to attend the nursery that will see them progress to the attached school. Childminder rates are around £3.50 an hour with discounts for your 2nd, 3rd, etc child.
Travel expenses. For a return train ticket to Glasgow during peak hours I think you're around £10 a day. Though buying a weekly/monthly/whatever pass ticket does save you quite a bit and would lessen the daily cost considerably. The bus is a good bit cheaper but obviously takes a bit longer and there is then the risk of getting caught in traffic.
Whilst your DH may not earn £30K doing what he does in London here, your cost of living would be dramatically lower. If he's in a professional role, you may actually be pleasantly surprised by the city rates he could get. There are always job opportunities in the cities. In the towns they are obviously less so, but I think that's true of anywhere.
I honestly think you need to consider a move out of London. London is a fantastic place to live if you're single and/or loaded. It's not so great when you've got two kids and earning £30K. The rents and childcare are extortionate. Days out are far too pricey. Commuting eats up whatever cash you have left and any hope of buying your own home is near on impossible because your rent eats up any chance of saving a deposit.
You sound like you're trapped in the 'London' way of thinking: I won't get paid as much if we move out.
You're right. London rates are better. But they come at such a severe cost, OP. Think about it. That premium London rate your DH is earning is going straight into everybody else's pockets but yours.
Please at least have a look at what else is out there. The north is lovely - I promise
Where about's are yours/DH's family? Would you consider moving closer to them for some support?