Bully child in the family is preventing DS from bonding with his grandparents.

I think a one year old is very young to be staying away from home without at least one parent. Obviously, not in an emergency situation, but at any other time. I remember leaving ds for a night at about 18months, but we had no choice.
You've been told 3 year olds aren't either bullies or mean. It's true. And 3 year old's parents will be learning just like you.
There's years and years of bonding time ahead. Why rush to overnights now? 3 year old is bound to treat grandparents place like home- that's what they've been taught. It's not personal. I'd treat them like a couple of puppies and let them get to know each other for short times, supervised, before I let them off.

This is the family you have and that your son has. It’s not going to be the same as the one you grew up in. You’re the one who lives far away from your in laws: you’re the incomers to that family, just like your DH is the incomer to your parents’ family.

Take it or leave it. If it’s really that important for your children to “bond” with his grandparents you’ll have to take them as they come. You can’t expect other people to change so that you can have the family environment you want for your son.

I say this only because the cousin sounds like a somewhat undisciplined toddler/small child. It won’t always be this way; I’m sure that isn’t the sum total of her value as a family member.

and given the story, that might be a fair comment

You might as well have just said ‘I don’t want my child to spend any time with their grandparents because I don’t like their other grandchild and I don’t like the parents of their other grandchild or the way that they parent’.

My nearly 3 year old is tall for his age and wears 4-5 clothing.
I'm forever protecting my 1 year old neice from him as he's massive and she's absolutely tiny, born premature too.
He has zero concept of personal space and will accidentally fall on her.
No way, I would leave those 2 together with just family as people seem to just let the kids play and sit back and watch.
So, go with your gut i would say.
It's all fun and games until he accidentally throws a hard toy at your child and you hear, oops it was only an accident, he didn't mean it.
Little comfort!

I do understand - and my DS was actually 2 years older than his boisterous cousin. Cousin was allowed to do what he wanted and the only time I ever witnessed his parents intervene before I did, was when he was trying to hit DS with a plastic cricket bat and his mum very quickly told him to stop "because he was too close to the TV" - no concern for DS.

As DS was older he was able to articulate that he didn't want to spend time with his cousin, so we kept visits to a minimum.

I think the problem lies with the parents and grandparents not laying down adequate boundaries, rather than the child themselves.

I would be tempted to say to MIL that a weekend sleepover sounds a lovely idea, but it's too soon at the moment as DS does know them well enough, and also cousin is a bit too boisterous at the moment, so hopefully by next summer cousin will have grown out of the boisterous stage and DS will be a bit more robust. Prod MIL into addressing boundaries with older GC if she wants younger GC to stay over.

I think the word you are looking for is unsupervised.

You sound quite PFB

I'd not leave a 1 year old with gp if they don't really understand they need to watch dc this age all the time. You wouldn't leave him in a playgroup unattended. Trust your instincts. He's too young.

Your description of a child of 3 is pretty concerning ...terrorising and bullying wow
The suggestion is a good one but if never recommend a child spends time with anyone who actively dislikes them as you do ....but one day you maybe pulled in to hear your child is now doing these perfectly normal behaviours it's the adults role to work on them....if your child ever hits, bites pinches pulls you I wonder how you will react because most children do at some point.

But as your not in a nursery/ big setting targeting one child isn't happening he doesn't have others.
Nothing in your posts say he has a problem...30 years in childcare...he's normal..
Parents of babies are naturally cautious nothing wrong with that...if you don't feel comfortable don't be pushed into it

3?

No. Dont send him.
Its not necessary at 1 to gave a sleepover with grandparents.
You wouldn't relax, so there wouldn't be any point.

I don’t really understand the obsession with children being forced to share.

I mean, tbh, I don't think it's wrong to acknowledge that some kids have less socially-acceptable impulses than others.

My son isn't a sitter. He's a runner/climber/explorer, and I've had to work hard to understand when and where that's allowed.

My friend's child is a hitter/fighter. At 18m he tried to wallop my newborn with a stick. At 2y he tried to crush him with a door, then squashed his baby sister deliberately. A month later, my son was crawling in his direction and he tried to wallop him with a spade.

I've never seen this child not trying to hit or otherwise harm another child. He doesn't do it with adults. It doesn't seem malicious, more "how will everyone react if I attack this baby?".

Basically "hitting" is their problem where "sitting" is mine.

But I think you have to intervene when it comes to your own child's particular issue.

The 3 year old is not a bully. You using that type if language makes me think you could be overreacting to typical 3 year old behaviour, it won't be good for your DC to be raised to be the type of child that sees every misdemeanor as bullying. Let him go to grandparents alone, it will probably be good for his social development.

A child that age can only display them for more than a few moments at a time if the adults around them allow it to continue.

But that doesn’t negate from the fact that it is the parenting and the situation that is the issue and not the child

Actually no, not all 3 year old are like this. My son certainly wasn’t! But then he was properly monitored, taught to be gentle, and had family who reinforced boundaries, none of which this child seems to have!

Having said that, he’s probably not doing it intentionally as a bully would. He doesn’t have the sophistication for that….yet! But it won’t be long if he’s allowed to continue being like this.

Not sure how old your son is but he sounds a fair bit younger. The grandparents won’t properly monitor either child by the sounds of it so no, he wouldn’t be going if he were mine.