AIBU to ask people with similar finances ..

Some people will have more income

Some will have much lower bills (eg lower/no mortgage, perhaps due to inheritance)

Some will be in debt

Some will have holidays and other extras paid for by grandparents etc

Some will spend a lot less day to day to afford holidays and cars

For many it will be combinations of bits of the above.

To pull a couple of points out of your post:

Monthly bills add up to £28500 a year (that does include £300 a month of extra curriculars and £100 of savings...but the savings always end up been spent on Christmas, birthdays and school holidays, so aren't accumulating)

Are you properly accounting for all your annual and irregular essentials and other planned expenditure in the £28.5k or does it end up coming out of the rest? Because that can make a significant difference and it could be that you're spending quite a bit on car expenses - insurance etc.

That leaves £280 a week for food, petrol, clothes, uniforms, toiletries, days out etc (1 adult 2 kids)

Depending on how much you spend on petrol, if you really do have £280 pw for those things, you could probably spend quite a bit less, given you could probably do groceries quite well for about £100 pw. If you could save £50 pw earmarked for a holiday, that's £2600 per year, which would definitely get you a summer week in the Med and possibly a weekend away at another time of year if you're happy to be thrifty about both, eg self catering with limited eating out and having easy food from the supermarket instead, mid range rather than high end accommodation, looking for deals on flights, hand luggage only, just spending most of the time at the beach rather than expensive theme parks etc.

Have you gone through what you actually spend to see if you can free up more money for things like holidays?

If you have no debt and a £200k mortgage, I think you are doing brilliantly.

Op, two earning parents are usually going to bring in a lot more, and the simple fact is these people just earn more, you’ve 3 people living on one salary basically.

don’t compare yourself, you’re doing well and don’t be jealous either,

I don't think it is helpful to see what others are doing without having any details about their incomes and other circumstances. They could be spending their inheritance, have much bigger earnings, grandparents could be paying for holidays. A new car to them does not mean a brand new car from the dealer. etc. etc. Not to mention that 45k split between two people results in lower tax contribution.
I am on 52k, childless and can't afford a luxury holiday every year because I want to enjoy my life every day not just two weeks a year and, where possible, overpay my mortgage. So holiday is not my priority at the moment.

Also don’t concern yourself with your peers - two incomes makes it easier to afford stuff - you also don’t know their financial situation- perhaps no mortgage/ rent - whacking it all on credit cards or have an inheritance.

£280 a week left over for food / petrol/clothes etc is just over £1k per month. Have you analysed what you are spending it on? I did similar and found a few culprits which I cracked down on which were costing a couple of hundred pounds a month.. I do earn more than you and only one kid but almost a teenager so v expensive.

edited to say also a single parent