To insist the holiday is cancelled

The child needing collecting at 3.15pm. At 3.15pm FIL arrived at the house having dropped MIL already at the school to collect the child. So presumably they were EARLY to collect. Not late. So no need to worry about the teachers ...

They were clearly fairly late (surely would have been at least 15 mins) for the school run (sure, that happens to me sometimes so not judging particularly) but it isn't funny - it's really annoying for the teachers.

It doesn't sound like they were late. By school dismissal grandpa had already dropped grandmum at the school gates and had time to drive home and get the car seat, so grandmum would have been waiting to receive the child when they came out of schol.

How did they get your key?

It's obvious you dislike your in-laws, but your reaction to them not actively actively offering your 2.5 year-old her drinks bottle that was sitting out in the kitchen through the day is unreasonable. Unless there are significant developmental delays you haven't mentioned your 2.5 year old is more than capable of asking her her water bottle or another drink if she's thirsty. And she won't suffer any harm going 10 hours at home without drinking if she's not thirsty.

In their favour, they had the wherewithal to sort out a way to pick up your DD, but they do sound very absent minded, and this was probably the easiest thing that they might have to do for a 3 and 5 year old.

If you don't feel happy leaving your children in their care, there isn't much point in going on holiday.

I wouldn't go on holiday and leave my DC for a week. Think it is perfectly fine that other people do but I wouldn't want to. And I especially wouldn't want to with young DC and people I didn't trust. They were clearly fairly late (surely would have been at least 15 mins) for the school run (sure, that happens to me sometimes so not judging particularly) but it isn't funny - it's really annoying for the teachers. I would also be annoyed if my DP booked a holiday without asking (I might not be able to get the time off work). I would cancel if I were you

Half the mums on MN fluster at the school pick up. Hardly a great benchmark.

I wouldn't go as they're too young to understand disorganised people looking after them. When they're older around 8-10 it'll be fine as they'll understand their GPs are forgetful and disorganised and they'll expect them to be late picking them up, will make sure themselves that they've eaten and had a drink. No doubt they'll help each other.
You shouldn't leave very young DCs with adults who won't be able to meet their needs.

To be honest they came through and used the car seat, which I thought was going to be what happened. The drink thing is a worry but maybe you need to give them good instructions and accept it might be a slightly chaotic week but they and the kids might enjoy the time together and you get to have a child free holiday. If the holiday is a way off then you have time to prep them.

The key thing is a problem but you should change the system so nobody can be locked in as obviously it is a fire hazard.

Arrange a different live in nanny for the week
Go on holiday

The holiday is next year?

when?

So the answer to my question is…

my relationship with them is not positive even putting this latest issue aside

They did, successfully, bring thier own children up … you need to unclench.

I also think there is the question will it cause tension if they do go

and was she persuaded into it in the first place

i think this will cause damage it it just controlling it as to where the minimal damage can be done

nowadays there are quite a few places that offer decent childcare including the evenings that could be a compromise

I couldn’t go on holiday for a week without my kids so YANBU.

They sound flakes to me, and I'm not a perfectionist by any means.

I've no time for ditsy disorganised people.

As others have said

Do you WANT to go on this holiday

Will it cause tension between you and dh if you don't go?

I'd be bloody furious if I booked a holiday and dh reneged on the grounds you're suggesting but if he's fine and understands then don't go because you sound like a worrier. You have to accept when you leave your dc with other people things won't run exactly as you'd like them to. They did the school run so I think you've overreacted on that score.

They said they would do pick up, and they did. They didn't organise it the way you wanted it, but ultimately they picked up on time and safely.
They probably didn't realise they had all the keys (locking when you leave the house does make sense to me).

Yes it's annoying they were not contactable, but that's something you can discuss ahead of the holiday.
Cancelling over this is overreacting IMO.

I don't get the "forgetting to give a drink". My 2 yo ask for a drink when she wants one, she has a own bottle available at all time in the living room and her bedroom that she can help herself to, and that's also how it works at nursery for children that age. I'm not after her constantly asking if she wants water...

I might be mixing you up with another poster, but was your husband also there the day that your youngest wasn't given a drink all day? If so, as the father, he was the one in charge and not his parents. More detail would be needed though before I could judge that occasion. Eg. No water given, but several bottles of milk is different to no water, no milk and only solid, dry food that day.

They made a mistake on this occasion by taking your keys, but they were responsible enough to collect the child on time AND collect the car seat, so I wouldn't judge them badly on this alone.

I think I’m more on the laidback end of the Mumsnet spectrum, as I don’t seem to be understanding the major issue.
Yeah, it was a bit chaotic, but it worked out in the end. And they’d step up more if you weren’t there.

Do you think you would enjoy the holiday or would it cause more harm than good to your relationship with both DH and your in-laws?

this type of decision is a personal one and one that only you can decide if you want to go ahead or not. Usually it is about 50/50 to those who could go and those who can’t with a week probably being even lower and a night away even higher! It depends not only on personalities but whether there are caregivers that you trust

and you don’t trist them for a week and it is as simple as that - is that an overreaction possibly. Does it matter - no

How did you find out about the drink? That is more of a concern to me than the school pick up.