We have a spreadsheet with all our incomings / outgoings, which we review often.
When we are paid we transfer a proportion to our ISA, SIPP and shorter term savings (holiday etc).
Then to our separate bills account to cover all bills that come out by direct debt.
We then have pots in our spending account for food shop, personal spends, travel, car, etc. When it's gone it's gone.
We are really strict and it's a bit miserable at the moment but I never want to be in debt / have credit again.
I stopped doing any top up shops and just get extra in the weekly food delivery as the local shops are 20% more expensive.
We meal plan, only eat out for special occasions, rarely buy clothes.
It's really tough with any amount of children, let alone three.
Edited to add we are building up an emergency fund too which is great for peace of mind but means we are actively going without day to day.