Cook from scratch.
Don't buy snacks. As my teen DD calls it, be an ingredient family. Snacks are fruit, cheese, nuts, homemade baked stuff.
Meal plan for the week and supermarket shop once per week. Ideally at yellow sticker time (around 8pm for our local asda) and ideally when you've already eaten (makes it easier to not impulse buy). If you buy yellow sticker veg, use it to make soup before it goes off. If you buy yellow sticker meat or bread, freeze it.
Have family meals, your DD eats the same as you and dh
No takeaways. Buy decent pizzas when they're reduced to always have in the freezer for nights when you can't be bothered.
When you go out and about, take your own coffee in a travel mug, a water bottle for the kids and your own packed lunch
If you eat out don't buy a meal for DD, just ask for an empty plate and give her a little from yours and DHs meals
Don't pay for expensive days out she won't remember anyway. Lots of stuff is free, parks, the countryside, the seaside, museums. Have picnics. Go blackberry picking. Call a trip out an expedition and make it sound exciting.
Buy everything you need second hand. Vinted, ebay, charity shops for clothes, gifts and homewares. Sell unwanted stuff on.
Find low cost playgroups to go to. Churches are best for this. 50p for a few hours, juice, cuppa and biscuits. Avoid expensive toddler groups like tumble tots.
Aggree with family to do birthday/christmas gifts for only the children, or a secret santa, or homemade gifts only to keep costs down
Cancel subscriptions or threaten to cancel and see if they offer you a discount to stay
Always shop around for insurance and utilities
Drive less, walk more
Use olio and too good to go
Think about finding a very part time job. Maybe wfh agency work?