To ask that my nephews don’t come

Lol at you accusing OP of being snotty! Your responses to OP are the epitome of snottiness and finger wagging. OP has been very polite to you.

You've planned a family event without 2 of your family. That's odd.

It would have been different if you'd gone for an event with you, your sister and your niece. That would have been a sort of grown-up adult or young adult afternoon tea and that would have been fine.

But you've muddied the waters by bringing your 3 young kids along. That changes the tone of the whole event and makes your nephews look left out.

I think you've made a mistake here op.

It's like a class party, either invite everyone or half the class. Don't leave just a couple of kids out. That's mean.

Fwiw my teenage sons would love an afternoon tea with all the mini cakes and whatnot.

So you speak to her everyday and then it was 'Whoops baby brain' - 'forgot to mention I'd planned a girls outing for 7 people'?

Like I said, there's definitely something you're not saying.

And whatever that is, it will be part of why your sister has reacted the way she has.

I’d cancel it and just take her out 121 or her and one of her friends

What has your sister organised for your niece's birthday? I'm assuming that she'll have organised a big family event for her daughter's 18th birthday.

She sounds pretty difficult and quick to take offence. Has your niece said whether she would prefer it if her brothers were invited? If she would prefer a 'girls only' afternoon tea, that is what you should do.

I think it would be a gift from the Auntie if it had just been arranged as an afternoon tea for the two of them.
The fact she invited other female relatives without asking her sister does suggest she knew it would cause conflict. It's also organising it more as an event rather than a gift.

I agree with the poster who has said make it adults only - I was surprised that the OP is taking her own young children (I presumed from the initial post they were female teenagers, not little ones).

That’s your cynical take on it. I see it as a kind auntie celebrating her nieces birthday. But let’s leave it there and not derail the thread.

She’s taking three under five with her as well, this is where the dynamic printable gets a bit confusing. FWIW I agree, leave your kids at home and just take your niece to a bottomless brunch or something else special.

Cancel it and invite your niece away on her own for a spa day or cocktail making class or away for a day doing whatever hobby she's into. Or day in London etc
Do it on a weekend so you don't bring all your kids keep it just you and her.

Sister opinion irrelevant on something like that as she's 18 and it's not a whole family thing or male/female only. And she can't control what her daughter can and can't do on a weekend just because she wants the weekends as family time only.

No but she doesn't have to drive a wedge into it either by playing the aunt that's more popular than the mum.

In no way, shape or form is it the OPs job to fix the relationship between her sister and her niece.

If it was just you and your niece I’d think it’s fine not to invite nephews, but given all their cousins and their mum is going to be there, it’s a bit odd to not invite them as it feels more like a family thing. Also a bit out of order you planned it all without actually speaking to your sister!

Yes, this is one of those times where I'd love to hear the sister's take.

I suspect there's a bit more than the OP is letting on.

It was a really lovely idea and a great way to celebrate an 18th. I'd probably have left your young children at home, especially the little girls. If bf baby and his dad can't have him then of course bring your ds but it'd ruin most decent afternoon teas and I'd not be happy if my afternoon tea was ruined by a baby, thinking of other customers.

So maybe strip it back to adults only then there's no contention about children being invited.

Otherwise tell your neice you will find a different treat for you and her as a gift.

This is such an odd take on it.

the gift from auntie to niece is an afternoon tea FOR her birthday, not ON her birthday (so mum still gets to organise the actual day of birthday celebrations - so no over-stepping). OP is paying so absolutely should get to say how many guests are there and she’s not inviting ANY males (including dads/uncles and the baby is irrelevant) so she’s not just excluding the nephews. OP is being generous by including her mum and sister as well as her niece to make her niece feel special. She’s also aware the the niece needs a little extra TLC at the moment. OP has been a lovely, kind auntie and sister and hasn’t done anything wrong. She can treat the boys on their birthday if she so wishes.

OP, I’d collect your niece yourself and go with your mum. Your sister obviously has something going on in her own mind which warps her take on your gift. And I really can’t see that teenage boys would even want to go and so why she would want to force them is strange.

But you said your sister is funny with events and only attends if all her kids are there - you booked this knowing that?

Of course I treat people, don't be so snotty.

But this is her daughter's 18th birthday. You took it upon yourself to plan this girls outing without consulting her at all.

Considering they have a strained relationship, why did you choose to plan it and then tell her?

I know you claimed 'baby brain' but was that the real reason?

Presumably more to do with the fact that it's a special treat for her, and shouldn't have to share it with annoying siblings, of any sex

I'm torn, it's nice that you want to do something lovely for your niece's birthday, but I hate overgendering activities.

Why wouldn't boys enjoy an afternoon tea? And the male equivalents always seem to be something sporty or adrenaline fuelled... what if the girls in your family fancy go-karting or watching a rugby match?

Normalising 'girls only' and 'boy only' activities just keeps outdated gender stereotypes going and puts limits both boys and girls.

I think it is odd that you have planned a girly day for an 18 year old that excludes her own siblings but plan to bring your own young children along. Surely a girly afternoon tea for an 18 year old should be a more adult affair?