To keep my three nephews up all night?

She's not forcing them to stay up all night, for goodness sake! She's offering them a night of fun without a strict bedtime. Of course they're going to fall asleep when they're ready to.

I think it is ok to let them fall asleep when they like but I wouldn't be giving a just turned 2 year old sugar late in the hope you can trick their bodies into staying up longer than they can physically cope with and once the 2 YO is asleep you need to make sure they are undisturbed by the older sibling and have somewhere they can sleep peacefully. I doubt the 2YO will sleep in like the older one did so you need to be prepared for an early start with a baby and crabby toddler or being up all night with an overtired toddler. If this is your first time looking after all three and a fairly young baby I would be making my life easier by putting the younger two to bed on time. You are likely to be up through the night with the baby regardless of what you do.

'It is not surprising that there are children out there who can’t cope with the slightest change to their routine due to the parents managing every single minute'

It isnt about managing every single minute it's about using some common sense which many sadly do not have.

3 kids under 6 don't need all nighters to have fun. 'It's not surprising' there's so many feral kids kicking about.

They’re not having an all-nighter, she’s allowing them to fall asleep together rather than putting them to bed. As a treat, as a one off, literally one night.
One late night does not make feral children.
Strict routines make children unable to deal with change and unfortunately change happens, children need to learn to adapt. By not having this life skill causes no end of problems for them in the future.

I wouldn’t do it for the small ones, just because I don’t think there’s any benefit. Babies and toddlers don’t really just keep on having fun until they fall asleep where they’re sitting. My experience is they just get continuously crankier and there’s a point where they’re so overtired and miserable that they can’t actually get to sleep, and when they do sleep it’s patchy and disrupted. I don’t really understand why you’d do that, it’s not fun or easy for anyone. Far better to have some fun and a nice bedtime for them, then go back to the oldest once they’re down.

I’d have no issue with it for the older one.

The screaming comes from overtiredness which leads to an inability to fall asleep which creates distress. It's not boredom, or not being allowed to do what they please, it is physical and mental distress caused by being too tired and not being supported to fall asleep. Falling asleep doesn't come naturally to all young children. I don't know how long you've been doing this with your older nephew but for my two they would have grown out of it by 5 or 6 anyway. It sounds like you think you know everything anyway so why not just crack on?

She knows those kids. Their mother knows those kids. You don't. So it's a bit ironic that your criticising her for thinking she knows everything. She knows more about those particular kids than you do.

Fundamentally, the children's mother knows her children, knows her sister, and knows and is happy with, the plan.

So while this thread has been an interesting read, none of the advice from others (and from the friend who is the subject of the OP) is needed.

I think you should do whatever is easiest for you. You are doing their parents a massive favour. But I would tell them what you plan to do

If course they watch feature films at that age! .
My grandchildren were watching films at the cinema when they were 3 as were my children.

Look after your own kids then, is the simple solution.

Why post then?

Tell the OP that then!

It really depends on the kids

My eldest would not have fallen asleep at any time before 3am (actually probably would have had a catnap about 10pm for 10 minutes, then woken again for hours), would have woken at the crack of dawn for the day and then been awful for days.

My younger one would have been fine. Still wouldn’t fall asleep till 2am, and be up early, but would magically manage on no sleep the next day. You wouldn’t have had any sleep though!

Sounds like your eldest nephew is a sleeper and will fall asleep at an ok time and sleep in the next day. All good. But you don’t say what the younger two are
like. If the parents are relaxed about staying up then they’re probably decent sleepers also.

Basically with decent sleepers this is fine. With tricky sleepers this is going to cause problems for a few days.

Some of the responses on here have really made me chuckle. Children are far more resilient than we make out. Even if they go to bed late and get up early, they'll still go to bed at their regular time the next day. I can't imagine they will be grumpy as the fun and excitement of an overnight with Auntie will carry them through. That's certainly the case when our nieces and nephews stay over. We all have a great time, go with the flow, try to herd them up around 10pm ish, sometimes it's later but the children love staying over and it's memories they and you will never forget. They are aged between 6 and 10 and have been staying over with us for years.

Wow this sounds so fun, can I come?!

Of course it's fine, OP. Used to have living room sleepover nights like this a lot when my children were little. Especially if their friends were staying over.

If the parents know your plan and agree to it, then that is the only opinion that matters. It wouldn't be my cup of tea for someone looking after my children as I think it is more for the babysitters benefit rather than the children's, but that is why we don't do sleepovers.

Fine for the six year old. With the two year old and baby..so unpredictable..could be a disaster, could be fine.