Have I failed financially? What is the norm?

I've been thinking of a way to ease gently into the 'talk' that you need to do OP and I'd suggest that you might tell everyone that having overhauled your budget/finances you are going to try a basics only month or two to get back on track.
This should be an easy way to curtail spending without the whole "I can't fund this anymore". Frame it as a reset, chat about finances and money saving ideas to them in a positive light & after a month say how relieved you are to be in a better position.
Hopefully by this time, a realistic picture of meeting up without bankrolling everyone will be the norm (and you can plan future fun without dread!)

Late to this thread... but I have four children and am still married, and could never have offered deposits for them to buy houses etc.
We are ordinary low middle folk. DH was in the RAF when they were little and so I stayed home because the youngest is disabled. We were broke.
Moved, and once the youngest was in special school I became a TA , which worked for us as I was home for holidays and of course DH was away a lot. It meant I never had a 'career' despite a good education , good degree etc.
Two went off to Uni and we sent them food money every week... that was tight. One lived at home until he emigrated and paid a token rent..£200 a month. His aussie girlfriend (now wife) lived with us too. Money went towards the bills.

Now, a few years down the line, only ds2 is at home. He receives PIP and that (with his agreement) goes into the household income as well as paying towards anything he needs, and towards us visiting his brother every other year. I've just retired from school, early as after 20 years my back is shot, but am earning a little in my own pet sitting business.

We now have some savings, but we have had to lend (not give) a lot of it to help my DD keep her flat after her divorce. I do child care to save DD2 from huge child care costs for her two. We are not wealthy...but it is more comfortable, less stressful now. However...when DH retires we will be poor again!

Mine do not expect me to pay for meals out..we share costs. They don't expect us to buy them cars (we did pay half for driving lessons but as teens they had to have part time jobs too). Two of them are in very decent well paid jobs now but life is expensive for them too.

It's ok to not be wealthy as long as you get by!
PS I hope you are claiming DLA for your son!

How does anyone ever meet up with anyone else that entails buying a snack or drink without the other person thinking that the suggester will pay?

Seriously ?
I mean, no-one I have ever met for a coffee or for lunch has ever assumed I would pay (no adult, I did sometimes take dc out when they were still at school).

If I am just meeting a single person then one of us would get both coffees, and the other would get the next 'round' be that on the same day or next time we met. Generally, for a meal, people either pay for what they have or split the bill in two (depending on circumstance). If our family met another family, before we got to paying one would say something like 'Shall we each sort our own families out?' and order / pay separately. I have never been in a situation where one person 'expects' to be treated just because the other made the initial suggestion to meet up.

I have a big age gap between my two children. My daughter is of an age where she has a degree, a husband and a graduate level job where she out earns me (her joint family income is about 3times mine - as a single mum, working- UC top up). She does have high childcare- but I only pay if I invite her out. My primary school kid needs more financially. She does understand this and never asks me.. although her dad is another matter as he doesn’t have young children.

My mum couldn't afford any of those things and I have real joy in being able to treat her as an adult! So you're not alone and I don't think it's having failed.

I don't think you should be forcing yourself to take iced coffee with you from home because you don't dare buy yourself a coffee in front of your adult children as they will expect you to buy for them. How long can you live like that for? You seem to be reluctant actually to have a discussion with them so that you can move forward with you paying for you and them paying for them. Why not just plan what you think is reasonable and then discuss it with them? Otherwise there will continue to be misunderstandings and resentment.
Sadly, it's possible that they will see less of you if you stop paying for them though. Do you think that's likely?

@Cantering87 DS is 31 and still lives at home but he’s not here very much as always off seeing friends etc
He buys half the food shop, pays me £350 a month plus the extra 25% council tax and is always very generous

I have never had to increase DS board as he suggests it
Meals out coffees etc are always split or taken in turns unless it’s someone’s birthday
Why not just try simple changes - next time in a cafe say do you want to get this one then it’s my turn next time
When I’ve less money I frequently just say I’m only doing drinks - if anyone wants food they can get their own

Myself and my partner have never earned good salaries- but we don't worry about money like that,but we never had children so maybe that is it.

If OP was on top up benefits, they would have reduced.

However, even when we have met at the park for example my children have said they would meet us and even with a picnic and blankets and my best efforts I still would like to buy myself a coffee sometimes and the younger ones an ice cream sometimes.

As an interim, on picnic days could you pack a special treat instead of buying coffee, such as a fancy iced coffee in a cool box or buy your coffee in a travel mug before you meet up so you've already got it. Same with ice-cream can you pack some fancy chilled dessert in a cool box as a surprise instead? Or have some nice ice-cream in the freezer ready at home to look forward to?

You shouldn't have to do this of course and your DC do sound entitled, especially if they always order the most expensive item, that's just cheeky when someone else is paying the bill.

I cannot understand the number of mums on here who freak out at the thought of charging their children rent. I paid from the moment I got my first pay check and frankly was quite proud to do so and upped it as my pay increased until I moved out. Paying rent and a share of the bills is good practise for later life, I grew up with my mum, sitting on a Friday evening totting up her budget, so was able to do similar when I moved out of home.

Have you ever sat your children down and explained the outgoings of the house, so that they understandwhere the money goes? It is an essential lesson and by their early 20s, I would expect them to be buying you the coffees, cakes and drinks. I think you need to warn them, that as of September, rent will be X, you will only provide the following, washing powder, milk, bread and butter... anything after can be negotiated.

I think it’s the expectation here from your adult children that you will pay that’s the problem! Both my parents and in-laws are reasonably well off and will often treat us however we would never expect that and always offer to pay our way and often will insist that it’s our turn to pay. Surely your adult children are aware of your financial situation and can understand that your can’t afford to pay every time you see them?

DD, early 20's in her first well paid job, told me she wasn't paying enough housekeeping and upped it. That was some time ago now, we're generous with each other, it's a nice way to be.

Your children sound like spongers OP, take a step back.

I don't think you guys are understanding.She wasn't literally saying she didn't have one pound.She's talking about the worry of giving one pound, it doesn't mean she's not charitable.You cannot all be this literal this is crazy. And the post you're referring to was rude enough that it's been deleted by mum's net.The fact that you are not able to understand why what she said was rude is actually your own cross to bear.

*I would never let my mother pay the bill when we go out to eat (typo).

Do you know what I honestly some people's responses on this are crazy, then I realise there are people like this, I call them the one pound crew they exist across all the society. They are in classrooms in our supermarkets. In our boardrooms, and they will never let things go, not one pound, not one penny.

I paid rent when I lived at home and my mum didn’t save it for me. Never held it against her or thought badly of her for it! Also I’d never let my mother pay their kids rent bill when we go out to eat… absolutely no way. Dad on the other hand, yhe he can pay sometimes, he didn’t birth me. But most of the time I pay.

If you cant afford it vs feel you dont want to pay for them then you simply need to tell them that.
Its about being honest and having firm boundaries
Its never good to do something you dont really want to, it always leaks out in not pleasant behaviours, the friend watching and laughing at your DC for example

It sounds like you are a people pleaser at your own expense
Pay but feel angry
" setting yourself on fire" to avoid a difficult conversation
However part of being an adult is speaking up and honesty ( you) and listening and understanding ( them)

Good luck @Cantering87