AIBU to be mildly irritated at this situation on Christmas Eve?

The traffic is diré Xmas eve better off at home.
As for the dirty house wouldn't want that at any time.

Erm hell no!
For what reason would you even think twice about not going?
Your family will get over it, it's pretty clear it's going to be the shittest Christmas eve ever and probably ruin Xmas day because the kids will be rushed to bed, and tired and cranky on Xmas day morning.
Nope!

Just tell them you’ll visit A earlier in the day but Bs will be too late and too difficult to manage with the kids.

I think it is. Hanging out with family, some food, excitement of doing pyjamas then getting in the car. Maybe my kids are weird, they always ask when they can next do car bedtime!

but I don't see 90 minutes as a long journey

@DappledThings it is on Christmas Eve when half the country will be on the roads.

I would go but I don't see 90 minutes as a long journey or why stockings etc can't be done before leaving. I'd stay till bedtime, get changed there then get children to sleep on way home and transfer. Assuming they will, if they don't transfer easily that's a different scenario.

Thats not exactly a lovely family Christmas Eve, is it?? I’m very pleased the OP has decided not to go

Just be very neutral. Something along the lines of "thank you for suggested Christmas Eve plans, it won't really work for us this year with the little ones, so we're looking forward to seeing you on.... " perhaps with a suggestion of when you can exchange any presents that need sorting.

It's ok for some Christmas plans not to involve absolutely everything, some things are less suitable for very small children and thats ok. You can have a lovely evening at home with your little family uni and catch up with family as and when.

This. Don't get into the stuff about the venue, just say it's not doable for you on Christmas Eve this year.

If people who know person B better are facilitating it at Bs house there maybe a reason for it that you are unaware of.

that doesn’t mean you need to attend, but just because it doesn’t suit you doesn’t mean that it shouldn’t happen there.

I can’t imagine many of the family would prefer it in an sanitary house hosted by someone with dementia, but if they are opting to go it’s probably because they understand why this is the best option for this year.

it still doesn’t mean you need to attend.

I can see you have decided not to go which is very sensible. But I don't think you should necessarily feel that they don't want you and that's why they are not accommodating your needs. Dealing with a close relative with dementia puts huge demands on the immediate family.

It could be that the B's children have seen such a deterioration that they are aware that this is likely to be her last Christmas in her home and they want to have the memory of everyone being around her. That doesn't mean it is your responsibility to enable it.

You should feel free to stay at home with your children and give them a lovely cosy evening even though you may be sad to be missing the party as it used to be. Sounds like it is time to start your own traditions. Something I never had the chance to do with my children as I was too tied up caring for elderly relatives.

Just don't go, I wouldn't in this situation

YANBU to skip anything tricky with kids that age. If I were you, I would call B to find out if they really want to host. If yes, then polite apologies that it's too much for the 3 of you this year, especially with all the annoying childproofing needed. If no, then offer to be the "bad guy" saying it needs to be at A's house this year to allow the kids to be put down for a sleep. Between you, A and B, you can work out moving this regardless of what anyone else wants.

Have a happy christmas either way!

It does sound inappropriate and unsuitable (timewise) for your young dc.

So just say that and stay at home, enjoy yourself with DC.

You and A do your own thing.

I would imagine my child has a nasty sickness bug on that day ……

failing that what about taking a travel cot with you 🤷‍♀️ and use it like a playpen , say you didn’t want the kids breaking anything and put a load of toys in ? Then it could be moved to another room for a nap later and you know it would be clean 🤷‍♀️

It sounds like someone has selfishly decided how they want everyone to spend Christmas doing what they want regardless of whether it’s the right thing to do or what B wants.

I can’t imagine someone with dementia coping well with a house full.

"Sorry if it's going to be at a late time and at B's house, we won't be able to attend. The timing would mess up our kids schedules too much and the house is not even clean enough for me to put my little ones down. It doesn't work for us this year but have a good time and we will maybe see about attending next year depending on what plans are in place"

Better to be honest and just tell them why.

I agree with everyone saying just don't go. Stay home with your little ones and enjoy it.

Exactly this.

Are yours the only little ones? They may not comprehend that it’s too late for them.

If B’s house is truly hazardous filthy I’d be making a phone call to adult social services because they need more help than they have and shouldn’t have to live in filth.

Just yes just decline make no big deal of it. Just sorry not doing three hours Christmas Eve with young children. Enjoy yourselves, maybe next year.

I can understand why they may want to meet at B’s - if B has dementia, a change of scene/routine can be very disorienting, not to mention with a lot of extra people and noise thrown in. My DM with dementia would not have tolerated it at all well -she’d have been very fretful and probably grumpy too.

So IMO you would not be in the least U for saying thanks, but no thanks. Quite apart for it being too much for your dcs on Christmas Eve, fewer people and less noise may well be much better for B.

I wouldn’t drive 90 min with two kids on Christmas Eve regardless of the house. A filthy house would be an absolute no.

Stay home and enjoy some festive things with your little ones.

If B is elderly and it is likely to be there last opportunity to have Christmas there, then I can understand their view.

I wouldn't take my kids (also under 3) to a late meal in anyone's house at bed time anyway, it would just be a disaster and there is no chance anyone would have a good time.

It's a one-off and an adults event, I think that's fair for them to want this and fair for you not to go. Hopefully no one will be resentful and you can organise to meet some of them at another point during the holidays.