To give parenting advice to SIL

Hmm it’s a tricky one. Safe sleeping and car safety are obviously very important but as pp have said, she will have had all of this advice and information from a HV and has chosen to do it her way regardless. I can see how you trying to correct her could rub her up the wrong way. Still, if god forbid anything happened to the child I think I’d want to know that I’d done all I could to try to help.

Basically you can’t change things and continuing to try to educate her will just piss her off so I’m really not sure what else you can do.

There are some guidelines that are there to ensure optimal development. Then there are others to ensure a baby doesn't die.

I really think that when it comes to the second type people should speak up about it. In fact wouldn't it be a moral duty? The SIL is actually breaking the law with the forward facing car seat - that's how serious a safety issue it is.

You're not wrong to say it. But sadly she was always going to respond like this. There is no way a parent in 2025 with so much access to information cannot know these things, but she chooses not to care. She chooses to believe it'll never happen to her child.
It's frustrating. I've had similar with a relative. You've tried- you can do no more.

This is true (albeit less likely than she does and just thinks it's too much faff) but even in this case, the OP should talk to her brother, who is equally the parent of this child.

She knows all this though, she's just concluded her baby is likely to be fine (it is) and she can't be bothered with it all

So you aren't wrong technically, but yes you are being unreasonable to offer your wisdom.

If you must offer unsolicited advice, direct it at your brother.

You can't just give that kind of advice unsolicited, it doesn't work it just makes people defensive or feel like you're sneering at them all the time. It helps IME to find a way to ask if they are open to advice but if they say no then you have to absolutely respect that. She has access to the exact same information you have and can choose to look it up for herself (which doesn't mean she is aware of it).

No, not everybody knows all the rules (IME this is a very "chronically online" assumption). And she may even judge you for things you do with your kids, maybe something that just doesn't even register to you or you think is nonsense. It's OK not to agree about everything and there isn't actually one right answer. Even someone's approach to following safety guidelines is not usually entrenched in law. (The car seat one is.)

But also, 99% of the time you can follow the exact opposite of the guidance and nothing bad will happen, so as much as these things look alarming when you've followed the opposite or it feels like an emergency, it probably isn't. The chances of something going catastrophically wrong are not 0, (hence safety advice) but they are low. The kinds of safety rules that we have for babies are useful but they are also based on population level results - common sense things like not throwing them out of a window don't even need to be said as safety advice because it's completely obvious. In fact, most safety advice is given as advice specifically because it's not obvious or might even be opposite to the obvious assumption, because most of the time nothing bad will happen when you do that thing.

I liked this article (not sure if it is a fully free one). https://www.cartoonshateher.com/p/if-you-didnt-have-postpartum-anxiety

I notice a lot of comments are saying SIL will know the guidance and is choosing to not follow it... this may not be the case. I'm a social worker, trust me, there are a lot of parents who do not know the guidance. Just because she has an older child does not mean she will know the guidance 🙃

OP, YANBU

You are completely right with what you are saying but someone like that is not going to listen to anyone

I wasn’t sure which way to vote - you are not unreasonable to think that your SIL is wrong and putting her baby in harmful situations, but I do think that she probably already knows the guidance and has chosen to ignore it (especially having an older child) so I don’t think you saying anything was ever going to change anything.

This is the most sensible response here.

You also have to remember that some of the guidelines we have here, although informed by science, are cultural. In Denmark, I saw loads of tiny babies sleeping in prams absolutely surrounded by big blankets and duvets. People in Denmark aren't stupid - the culture around baby sleep is just different (and most babies don't die as a result, because as this post points out, it's increases in tiny risks we're talking about, not guarantees of harm).

Either way, you won't be giving her info she doesn't already know.

Well, she’s risking her child’s safety. She’s either irresponsible and uncaring or head-numbingly stupid- either way she’s not going to thank you for pointing out the risk she’s taking.

You did the right thing though. The sleeping arrangements - the pillows, duvet, teddies - and the loose harness were both completely unacceptable risks, with the possibility of immediate injury or even death. Very different indeed from letting a child eat crisps.

I think this is it. When giving parenting advice, I think you have to be uber sensitive and tread incredibly carefully. I’d be worried about the pillows etc too but I think you have to gauge whether the person knows this is not recommended, and she clearly does. Experienced parents do have more experience of expert advice changing back and forth over the years so likely to be a bit more skeptical. It’s a fine line and your feelings are valid but it does sound like you could have managed the scenario a bit more skilfully.

Someone posted a picture on a very big extended family WhatsApp of their baby sleeping face down on a sofa cushion at a big family gathering. Third baby. Grandparents uncles aunts. Not a comment except complimentary. I was thinking oh my goodness but I didn't say anything why would my opinion make a difference if so many people thought this was adorable practice ?

I think the difficulty here is that lots of people don’t follow the guidelines you’ve described; they don’t get arrested and their kids don’t get taken off them. Her kid would undoubtedly be at less risk if she did as you have suggested but in all cases, the risk of suffocation is tiny.

You’re not wrong OP but lots of people do differently to you and that’s perfectly acceptable (I mean there is no law against it).

About the safety of a tiny infant? In fact, one which is in her family and which she knows isn't being looked after especially well? Most people would be invested.

You can win the battle by pointing out her errors but lose the war.
As someone said upthread everyone knows what is safe or advised but they choose not to follow the guidance. The WHO suggests breastfeeding for up to two years, a very young baby isn't meant to be in a car seat for more than an hour, children arent meant to drink milk in the night after the age of one. Co sleeping is not advised. No TV for under twos. Dummies in toddlers are bad for speech. We all know people, or ARE people who don't follow this guidance.

The best way to influence people is to be friends with them and quite often they copy what you are doing, if they like you. Ideas filter through naturally through peer pressure.

So I suppose just pointing out to her what she is doing wrong isn't going to be as effective as modelling your own better way of doing things silently. Post photos of your child snugly strapped in with a blanket. Of a baby lying in his new safe cot on a flat mattress with no teddies. Enjoying a teddy on your lap. Like we all knew it was bad to give our toddlers chocolate biscuits but believed that mini rice cakes were good. It's peer pressure that works not criticism.

I find it difficult watching babies being carted around in car seat systems instead of lying flat in prams. I say nothing. Maybe I should

No, it’s because you sound so preachy and despite the poll saying YABU you are completely refusing to see any other of things and just gushingly responding to people who agree with you.

Overwhelmingly people will think what your SIL is doing is wrong but you seem to be persistently and consistently (and mustn’t forget kindly) pointing out everything you disagree with.

You’ve made your decision to allow your child to watch tv and eat the baby equivalent of junk food at his age, despite the evidence suggesting otherwise, and that’s your decision (I made the same one at some point with some of my children, so not judging) but I doubt very much you want people self righteously pointing it out to you.

Because she's the only one doing any parenting by the sounds of it. He sees it as "her job", apparently.

Advice on something like screentime or food choices I’d say YABU, but the idea of a baby having a pillow and being surrounded by teddies honestly makes me shudder. YANBU.

You have done what you can. All the advice you have given is correct.

Now all you can do is hope that none of the risks she and BIL are gambling don’t pay out.