To have nothing further to do with them?

Are they still downstairs having a cup of tea with your DH? If so, why not take a deep breath and go and talk to them like the adults you supposedly are, because this is getting really out of hand and it will impact your DH, your PILs, future gatherings like Christmas and, most importantly, it's going to impact your child because there will be no going back from it. Calmly explain that you are hurt because they got their child to lie and you don't know why and would like a reason for it.

I think this explains a lot about your reaction here - most NT people would not be so black and white in the way they treated someone as you are being here. You’re upset because the other parents are not facilitating the sort of relationship you want between the cousins - without realising that your child can have a lovely relationship with his cousin but on terms that both parents want. But the more you push this very intense relationship dynamic - or overreact when they don’t do things the way you want them to - the more they are likely back off. It sounds like you’ve felt excluded a lot in life so you are reacting based on your own hurts - you need prioritise what’s best for your child. Making this a bigger deal than it needs to be and in the process hurting what could otherwise be a nice if more distant relationship for the cousins is not fair.

They are family rather than friends, what have you done to make your own friendships or facilitated friendships for your child?

It's quite telling that you say this relationship is important and you want them to be close, yet the moment there is a bump in the road, you give up and flounce off.

It's very normal for cousins to branch out from each other once they're at school. They get their own lives and interests. They could have still had a lovely family relationship, just not at the level you wanted. But now with your tantrum, they may not be able to.

My brother and I have several boys between us, all similar ages. We used to go to parties and see each other a lot when they were little, but that petered out as school life got in the way. They still have a good relationship, but don't see each other nearly as often.

Surely it was a "friends/school class" party rather than a family one. They even came over to celebrate you with you and DC!

Also - I'm not saying this is relevant here - but I have a niece that I loved buying things for, meeting up with, to visit places with my DC. Unfortunately, I haven't done so in the last few years because her parents consistently cross boundaries, are very entitled etc etc... and I've had to pull back.

Unfortunately that affects my DC's relationship with her too.

You are not taking anything anyone is saying on board are you?
You are projecting your own experiences onto your child
Sounds like you don't have many friends yourself but you need to encourage friendships for your child at school or clubs rather than blow up family remtionships over some percieved slight

I imagine they've changed that. I would have done.

You've dialled up the situation unnecessarily.

This is massively harsh and quite out of order.

I feel happy to judge an NT society when it has been my experience, yes. In my experience NT people can be really cruel to others. Then they say that autistic people have no empathy. Which is funny.

Ask them.

Jesus.

My child’s 7th birthday cost me about £20 on art materials, stickers and craft stuff, £10 on cake and baking supplies, the price of a couple of takeaway pizzas (could do cheaper and cook yourself) and a multipack of fruit shoots. Five kids has a great time in my dining room and went home with a cupcake they’d decorated, various pieces of artwork and a bar of chocolate.

You do not need to spend £300 on a party, but if you want Mum friends and your child to have class friends it might be one way to make the effort.

Some of these responses to the OP are really mean. She has told you all that she’s autistic. Maybe she has RSD? This is quite common in autistic people. Luckily I don’t have this. But for some autistic people it can be a very upsetting thing to live with.

@PouticelI don’t think AIBU was a good place to have your thread. Maybe move it to relationships?

I find it interesting that you feel happy to judge NT people but don't like it when it's done to ND people.

Mostly, people are ok. The OP has clearly contributed to the non relationship here, it's not all on the cousin's parents.

You are trying to force a relationship and then behaving really badly when it doesn't go the way your idealistic picture in your head went
Its nice the cousins get on when they meet but you are over the top

There’s never no reason.
your reaction today is giving them a reason on a silver platter. If you e not bothered to find out what the problem is or to fix it, how can you even hope the kids will be close?

This seems to be about your own issues that you should probably work on before you affect anymore of your child's relationships.

People normally lose their parents well into adulthood unless there are tragic circumstances that result in loss of both parents at a young age or their parents are much older when the children are born. By this time alot of people will be married, have a partner and often children themselves. Many people choose friends to spend Christmas etc with. It is not inevitable that an only child will be alone at Christmas. Even if your child was in this situation, her cousin may live far away or have her own family to focus on.

You cannot control other people or dictate their values. If their outlook on life, priorities or values differ from yours it does not mean they are cruel or bullies.

One of the most important and most difficult things we can do for our children is to examine our own demons and model positive behaviours including resilience, healthy communication skills, how to express emotions in a non-harmful manner and let them see through our responses to life events that our self-esteem doesn't have to be dependent on other people's perception of us. I believe that's how we support our children to build healthy, sustainable relationships.

Your in-laws probably find your neediness and thin-skinned intensity exhausting and don't want more than the bare minimum of exposure to it, for themselves or their child.

You sound like a spoilt child, OP, and very petty. Things change as children get older, and families don't need to live in each other's pockets.
There may be very good reasons why they don't want to spend time with you!

I can totally understand why you suddenly had enough. I think you’ve realised that they’re never going to let DC have a meaningful relationship anyway.

How have they reacted to you leaving the group, not being there etc? Have they said anything to DH or PIL?

I’m autistic, too and so are 3 of my children.

I learned years ago to only socialise in
spaces with other ND people. And you can tell where these spaces are - you can tell who you fit with. It has been a very welcome modification to our lifestyle because NT people get on my nerves - the falseness. The saying one thing and meaning another. The bitching behind people’s backs and two-faced attitude. Its a dog eat dog world that causes MH issues for me and my kids.

My 5 year old and I just had a really nice summer holidays doing fun stuff with other people who like and appreciate us and whom we just gel with. I found a school, dance school and swimming club where we just fit.

Are you only reading reply’s that agree with you. This won’t help.

The didn’t want you to take their seven year old on holiday! That’s fine I wouldn’t want my seven year old to go on holiday without me.

They obviously had a class party. That’s also fine and their choice.

They are not saying they want nothing to do with you. Please go rejoin the party