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

Personally I wouldn’t send my 1 year old to stay with relatives he hasn’t spent much time with for a whole weekend, a day trip, with them taking him somewhere would be much nicer.
I think by now you probably regret using the word bully, as 3 years don’t tend to bullies or mean for the sake of it. What they do however is lack boundaries, impulse control and need switched on adults to help them socially interact with other children, especially ones smaller then them who aren’t as physically able.
Its their parenting choice to give them fizzy, sweets and an iPad and you are being judgmental bringing that up, however you are right to be concerned that a 3 year old is not being adequately supervised whilst dealing with a younger child and is allowed to snatch things of him and potentially accidentally hurt him by knocking him over etc
I wouldn’t mention at the moment the three year old, I would say due to the age of your child and lack of time spent there alone, you’re a little anxious about him staying there for a weekend and would they you to book a Christmas lights experience or similar that they can take him to.
Worst case they think you’re an over anxious parent and may mutter that they want to spend longer with him alone but ultimately he’s your child. Telling them that their 3 year old Grandchild on their maternal side (I read it that it was their daughters child) is a fizzy drink swilling bully will not win you any favours!

Who on earth gives a toddler sweets packed full of refined sugar amd additives and then stands back and wonders why they are behaving like they are out of control?

Who on earth gives a child of this age sweets in the first place? And fizzy drinks that will rot their brand new teeth?

The issue is not the child.
The child is only responding to its environment and stimulation through sugar based products that are not designed for such a young toddler.

@shakercream I honestly have had this exact situation. Slightly older cousin but basically there all the time my 1 year old was there. Was so rough with her and not GPs fault but the parents never set any boundaries/consequence

How did that occur though? Did you just leave them there or were you there and just sat there and did not intervene? I find that mystifying either way. All my kids are adults but I still intervene if somewhere with kids that age and other adults are not doing the job of supervising/intervening/redirecting etc. You don’t need to yell at toddlers or hit them, just intervene, try and redirect and if you can’t then control appropriately. The worst that happens is a tantrum and I couldn’t give a shit. If a parent wants to complain, I’ll give a double serve back re their shit supervision and parenting skills. If you want to keep relations ‘nice’ for whatever reason, just badge it up as ‘giving you a well deserved chance to kick back and relax, and I’m watching them so you can have a break’ as that then allows them to save face.

You can say no all you like. Having worked with young children for many years and knowing lots of 3-4 year olds, the word “bully” fits some just fine.

When we go away, my parents or PIL stay to look after the dog and sometimes the kids too. The only room that doesn't have a single bed is our room, so they stay in there. I'd prefer to have a spare room for them but we don't. This arrangement means we get a free dog/babysitter so it's worth the slight weirdness. I think it would be worth it in your situation too.

That's why walkers cause so many accidents I hope you got rid of it they shouldn't be used on smooth floors or with steps.

The 3 year old wasn't at fault it's what they do.

Op whatever happens I always say people judge how people parent at gps etc, the thing is when you’re at family homes things are different, it’s a bit more relaxed, you’ve other family members to give you some respite plus it’s a treat so yes they get sweets etc (not a fan of fizzy drinks for that age but …) so I don’t love people judging when parents could be exhausted and chilling at family’s homes

The thing is OP that it only takes a second for an accident or injury to happen and that environment doesn’t sound safe for a one year old to me. The GPs and in-laws sound very hands off and anything for an easy life but that win’t keep your child safe from a rough poorly raised older child (not child’s fault obviously).

I think inviting them to your and going out for a half day leaving them in sole charge and building up to night away is a better way to build bond. Or visit when you know other child elsewhere (nursery?) for a less complicated time together. No I don’t think it’s weird to use your own bedroom for guests (that’s what my DD does when we visit to babysit).

The most important thing is always keeping your child safe so that helps clarify your decision making but I know it’s complicated with family.

It sounds like the PILs aren’t able to manage looking after young children so no I wouldn’t send a child there for a whole weekend.

Why would you want to send your small child to a frenzy of fizzy drinks, sweets and screens? And to be occasionally bashed by another sugar fuelled toddler? There is no actual parenting taking place of any description, and this would be the last place I would send my child for any other reason than an unavoidable medical emergency (and I couldn’t find anyone else!)

Bonding is an organic process of many years. You can’t force it.

3 year old aside, I would not personally leave a 1 year old with adults they don't know well for an entire weekend - even if they are grandparents. They need to get to know them first, to feel comfortable and secure with them. Add to that your misgivings about their ability to supervise and keep your child safe without you intervening - it would be a hard pass from me. I'd try to increase your visits together, and they can stay over when they feel more bonded already.

The 3year old is probably hyped up with fizzy drinks and sweets .I would be more concerned about that.

Your title is harsh and misleading. The child isn't a bully and he isn't preventing your son from bonding with his grandparents.

This is a very weird take when talking about very small children. Obviously you don't want anyone to hit a 3yo, what's wrong with you?

My own dc have survived to their teenage years without "hitting back" or, in fact, hitting anyone at all. Teach your dc to know when to seek adult help instead.

The 3yo isn't a bully, they are three! Your issues is clearly with the gps late of ability to supervise, I guess, but blaming a small child is really off. Their brain simply isn't ready to empathise and control their impulses as yet.

Those adults need to step in to manage the 3 year old behaviour, not reward it with fizzy drink ( his teeth !! ) sweeties and iPad !
he’s just being a 3 year old but an unmanaged one .
I wouldn’t let your little one stay without you there until this is manageable

So meet them half way between for days out.

I honestly have had this exact situation
Slightly older cousin but basically there all the time my 1 year old was there
Was so rough with her and not GPs fault but the parents never set any boundaries/consequence
My pp anxiety was so high in the first year
People told me it's fine and not to worry about it and I did leave them there a few times as I thought maybe this is just my pp anxiety getting the better of me and my DC got pushed around, things thrown and hit them etc, trying to bounce them too hard in the jumperoo etc, touching her when she just had surgery in the exact place I just told everyone "don't touch her there she's had surgery"
The sad thing is now my DC is 3 and absolutely now hates going to GP house. Says "I don't want to go there. " Or even "it's scary there" Or will say "no 'Oscar', just Nanna there"
So now we barley go round as she doesn't like it and it's all down to that first year. I try get the GPS to come here but they are so tied with obligations to the other grandchildren it's harder for them, I'm sure in an ideal world they would love us round there more but it's just not worth the aggro.
The cousin is older now and doesn't bother with her now but shes got those memories ingrained and they are stuck there from her first couple of years and that's it, her mind is set and it's affected the bond with that side of the family

Well, I do agree that they're "learning to share/want all the attention" etc.

But the majority of toddlers I know age 1-3 are all variably able to share, and especially want each other's attention (which is not to say they're good at it).

If the parents aren't supporting that learning, it won't happen at all. Where I live, every toddler is being followed by a parent intoning "you have to share", often contradicting another parent saying "don't snatch, that's not yours".

It's a bit mealy-mouthed to say that 3yo are still learning if nobody appears to be teaching them.

3 year olds haven’t learnt to share yet. The issue you have is with the grandparents. I don’t know how old your child is but there is no way I would let my child stay with them if this is how they care for the 3 year old. Why on earth would you think that’s a good idea? If you want them to have a relationship invite them to yours or for days out. Problem solved.

The other child is 3. All 3 year olds are still learning to share, be kind, want all the attention etc.
Surely this is an opportunity to build relationships between the cousins. They could end up best friends later.

In which case invite them to yours and you and other half go away for the night - the one year old has their home surroundings, you can hide the iPad etc and the grandparents get their 1:1 time

So not the same situation, but I do have a friend with a pretty violent toddler, and separately, my parents live a long way from us.

On the first issue, yes, whilst he's little, I just limpet on to my son when he's with the rough toddler (this has been going on since DS was a newborn - whenever I've met this child, he's tried to hit or bludgeon my son, and is very rough with his sister too). My friends "gentle parenting" doesn't seem to be the right strategy, but I just meet them and make sure I'm on hand to intervene.

So no, you don't have to leave your 1yo at the mercy of this child. In another year or so, he'll be much bigger and more independent.

On the bonding issue, my parents live 200m away, and see my son 4-5 times a year for a few days at a time plus facetime. He's 2 now, and he asks after them, chats with them, and asks to call, just as much as the local grandparents he sees once a week

He even asks after my mum, who quite frankly semi-ignores him half the visit, whilst my dad is hands on all the time.

So no need to panic about bonding.