No job, regardless of the extra income, is worth crying at or over. You'll have saved yourself a huge amount of stress and possibly worse mental health issues as it would be unlikely to have got better.
It's a good time to be looking for work as there is a huge labour shortage, particularly in the hospitality sector so I'm sure you will be working again soon (if that's what you need/want).
In the meantime check out "entitled to" to see if you are eligible for any additional help (e.g universal credit top up).
Your unhappiness at work, and worrying about it when you weren't there, would have impacted on your children eventually, if not already. They will be better for having you happy and with less work-related stress you'll have more patience
and more time with/for them.
Long term you've made the best decision for you and your family and will find another - better - role. Ignore the snide posts suggesting otherwise.
In the short term I know £400/mth is a lot to lose, but some decent budgeting and planning ahead now will minimise the impact. Reduce any 'frivolous' spending, ask for a temporary overdraft, switch to 0% on credit cards if applicable, change to a cheaper supermarket/market, meal plan and prep, buy a few Christmas gifts now to save a panic buy later on, change to a cheaper phone contract, sell unwanted items on Facebook marketplace, reduce any pocket money - all these things, and plenty of other small changes, can all lessen the worry of reduced income.
Best wishes and good luck, it will be ok. If you'd stayed at that job everything (apart from finances) would have got worse.
If you have a DH/DP I hope they are supportive as together you will be stronger and any 'lean times' will be easier.
If you're on your own you'll almost definitely be entitled to some additional financial support (like universal credit, free school meals, possibly housing benefit and councils can pay the shortfall amount via DHP, discretionary housing payment) until you find a new job.
You've got this - don't panic!