Am I unreasonable or is MIL

You are being too controlling. It’s fine to be flexible if they’ve arranged an impromptu thing with cousin and it looks like your son wants to go. Nothing wrong with that🤷🏼‍♀️

But it is unrealistic and foolish to cut off your DH family. It is an unfortunate situation but nothing you can't eventually resolve . Her husband probably got ill and flustered listening to her hysterical ranting . No need to escalate the drama just bide your time . Maybe your DH could have a word with his sister to diffuse things.

This is a very good response. Don't internalise other people's poor behaviour as your problem. Her intense overreaction is wholly her responsibility and it's her baggage to carry. A further PP above has it right: she's deterring you from asserting boundaries by making the consequences very unpleasant for you.

Because we're human, falling over ourselves to apologise is often people's first reaction when faced with an unexpected barrage like this. But it's far better to make them own their behaviour.

Finding alternative child care is a good way of making very sure she doesn't do it again. Glad to read your plans to do just that, and also of the fact that your DH has your back.

She will now be the one feeling the consequences of her own behaviour. As, indeed, she should.

Agree with this. I would not want to be beholden to someone like this for childcare. Her behaviour is irrational and I'd not want this kind of unpredictability adding to the stress of my working day.

To allow her to go ahead with the plans without comment and then raise it later was a forbearing and tactful response.She was able to do what she'd arranged anyway, so I don't see the problem. You've also done nothing wrong in raising this by text. No doubt she'd have reacted badly no matter what the medium of communication, and I wonder if something inside you sensed this beforehand.

Whatever the situation, your message has certainly opened the floodgates and a lot of the resentment she's clearly been harbouring against you has spilled out. Proclaiming that you've always hated her is a pretty strong statement and unlikely to have come out of the clear blue sky. I'd take a step back, organise alternative childcare, and allow your DC's other parent more of an active role in communicating with their side of the family. You don't have to tolerate abuse like this.

The extreme reaction is designed to deter you from asserting a boundary again. Don’t let it.

I’d make Dh deal with this. Make other arrangements for childcare and don’t rely on her again. If the way you’ve told it is the simple truth, then she is either a serious narcissist or has other serious issues.

Does your MIL make plans like this regularly, or was this pretty much a one off? If it was a one off, I personally wouldn't have said anything and certainly not by text. You say FIL is OK now, but perhaps she got herself in a state about him. I don't know how old she is, but you do get more overwrought about things when you get older which, I appreciate, is hard for someone younger to understand. Did she feel under pressure from SIL, what's the dynamic there?

You haven’t done wrong at all. Some people are literally unreasonable. And incredibly dramatic.

Ive had a similar situation. I just maintained being a grown up and then kind of told them off the next time I saw them in a “really disappointed” tone and arms crossed.

I said something like - “Im actually really disappointed that you would turn against me so quickly, I thought we had a really good relationship but clearly I got that wrong”. Funnily enough they were very quick to dispute that and argue that we DID have a good relationship and started digging themselves out of their hole.

Confused first of all why you weren't invited! My MIL would invite me but probably only 75% of the time I'd accept and I'd let them drop him back later and enjoy their plans. Very rude of her to tell you so late and then to suggest you make an additional trip to collect! There's obviously been some friction before this point. I wouldn't be seeing them again unless I had an apology and also be requesting an extra day at nursery on Monday morning and booking annual leave on their next scheduled day.

OP says MIL pushes boundaries and that MIL is doing childcare because she wanted to and OP’s child was in paid childcare before this. This incident was the first time OP stood up to MIL and now MIL has lost the plot and sent messages berating OP over her reasonable request.

I think this is sensible advice.

It was really thoughtless of her not to ask you if ds could stay for longer that day and go out with his cousin. It was thoughtless because you had a pointless trip.

But would you have said yes if she'd suggested it? That's what you have to ask yourself honestly.

In the text she is saying that FIL is unwell because of your behaviour and that she knows you hate her, that doesn't kinda suggest some sort of back story?

YANBU

Definitely go back to paid childcare. A tantrum over a gentle reminder is bonkers. Bet she wouldn’t have acted that way if her son had sent it.

There’s always one, isn’t there? 😁

Until you can source paid care, your husband needs to take over all contact with his unhinged mother.

Huh?
That’s not how I read the situation at all

Glad you've decided to go for a paid carer. She sounds unhinged. Next time (if there's a next time) I would not bend, take son home even if he is disappointed. She is a boundary pusher and completely out of order to attack you for making such a reasonable request.

Are you the MIL?

Can dh pick up instead? If he wants the saving of childcare. What is your journey time from pickup to home? Are you just down the road from MIL? Because unless you are neighbours, it is really rude to have someone come to pickup and be turned away at the door, you’ve worked all day, you do not need this extra pointless detour.

Agree with all of this.

if your DH is happy for his mother to keep doing the childcare, then i would push the entirety of it on to him, he collects DS, he picks up if ill, etc etc

Step right back and let them get on with it.

In which case I’d step right back and let him deal with her from now on.