Mum says Christmas was too much for her and I forget she’s getting older

Just ask mum to tell you what she would have preferred. If you can accommodate it do. If you can't as it will make the day rubbish for the kids then maybe spend Xmas eve or boxing day with her next year and have Xmas day how you want.

She doesn’t want to spend Christmas alone in her room..

This. Other people’s children can also be very tiring however much you love them. OP, perhaps suggest she takes some time out in her room watching a bit of tv if she finds it too much. Maybe she feels she needs to be present the whole time but you could reassure her she doesn’t.

I think people are focusing on the neighbours because she was obviously up for spending the day with you and your children, maybe the neighbours were a surprise and required effort to then socialise with others who aren't immediate family.
But it is your house, and sounds like you were a great host for the day.

OP has said that her mum has a whole floor to herself in OP's home, with her own bedroom, bathroom and TV. She could have excused herself and gone upstairs for a rest but she didn't. She just complained about everything afterwards.

It sounds a lovely day, and if you are right that the kids are the issue then she just has to suck that up really doesn't she!? No one should be trying to make Christmas day less centred around kids! The only things you can do is make sure she has somewhere to go to for quiet, which it sounds like she did, and ensure she knows she is welcome to do that without offense. You can also avoid asking her to 'mind the kids ' too much I suppose, although if it is when you are cooking or cleaning up Christmas dinner, it doesn't seem too much to ask! If that's not enough,

If she's genuine about liking the neighbours being there, it may make things worse if you didn't invite them again, as they probably help reduce the attention kids are demanding from her. I know my mil said she finds it easier when the other grandmother is also there for that reason!

Apparently, OP's mum enjoyed the talent show and she sang a German song. OP has said that she actually doesn't enjoy being with her grandchildren and wishes that the day was adults only.

As OP's mum doesn't have any other children, unless OP puts her kids in an orphanage, the only way her mum can have a child-free Christmas is to stay at home on her own. It's her choice, but to moan about Christmas Day is rude and ungrateful of her.

Fair enough. Missed that somehow.

Her choice for next year is a child-centred Christmas with you, or she is free to find others to spend an adult Christmas Day with. Her having no other family absolutely does not mean you change your Christmas to some children being seen and not heard nonsense to suit her. And yes, she has limited remaining christmases and you’ll miss her when she’s gone, but you also have limited remaining magical christmases with small children.

I am 75. I went to lunch and Christmas festivities with my step-son's DC and their DC. There were nineteen of us and DC quite excited (mostly excited earlier and calmed down). We exchanged the gifts that Santa had brought to the wrong address (two DC under 7) while dinner was cooked. We played a game after dinner and got variously tipsy. I enjoyed it.
Perhaps asking your mum to play with DC is a bit much? Personally, I'd rather help with the washing up! I have done my bit with playing with DC (though I occasionally do it) and perhaps your mum feels the same.

This exactly.
You can see your neighbours anytime.

Except the OP said

i’ve tried to ask her more about it this morning and it does seem to centre around the kids. Say she loves having the neighbours over because they’re such nice people and really enjoyed the talent show because she got to sing her German song

Basically she wants the kids to be seen and not heard and everyone to focus more on her.

She sounds inflexible and unreasonable. If she had a whole floor to herself with her own bedroom/bathroom and TV, she could have excused herself and gone to her room for a rest.

It is your children's home and they should be able to enjoy Christmas Day without you being worried that they are 'too much' for your mum.

This. The “talent show” sounds a bit full on, too.

I was thinking the same! I’d not give it another thought other than to say she’s welcome to spend more time in her room rather than joining in, if she feels it’s too much (or not going to yours at all).

I certainly wouldn’t be changing giving your kids a magical Christmas because your mum finds it too much.

Offer to take her home after lunch next year. You can drink champagne once she has gone, and enjoy a party! I think you can agree a different plan without it ruining yours and the children’s fun!

I think she would have preferred no extra people, just you and your children but it's not really her house to dictate that.

Yes, I’d have taken myself off. I wouldn’t expect the day to be tailored to my needs. I understand the drained aspect but that’s my issue not theirs.

sounds like a very quiet day to me

but when you are a guest in your own child's house, no one stops you from going to your bedroom for a couple of hours nap/ rest.

You can't do that when you host, but if she found it too much, she could have just disappear and rest.

If she doesn’t see or is around young DC much during the year, the noise and chaos of them at Christmas could be overwhelming. Not saying DC have to sit quietly all the time she is there, but give her more options in the day to opt out of their play without seeing it as rude

Op - my parents are 75 and 66 - they would also dislike the neighbours being there, but would be too polite to say anything.

You do what you want, and more importantly what your DC want. You don’t need to scale down anything IF you don’t want to. She can choose to be a part of it…or not. Her wants don’t trump everyone else’s. She’s ageing and this attitude may escalate and not only to Xmas. Set a precedent.

so she can stay at home and have a bit of peace and quiet.

If she wants to stay at home and have a bit of peace and quiet, then she can stay at her own home and enjoy the peace and quiet there.

It’s batshit to expect others to vacate their home with their kids on Christmas Day so that you can relax.

If she needs accommodating to this extent, then she really needs to stay at her own home. The OP has young children. Their enjoyment of Christmas is the priority.

Well , hopefully, you’re capable of managing your own needs , or at least able if expressing them, rather than expect people to mind read and then act accordingly.

There is a time and place for honesty as well.

It's incredibly rude to go and stay with someone for Christmas and then tell them you had a horrible time.

You're entitled to your feelings but it's your responsibility to manage them and to be tactful and kind about it.

"It was all too much for me, I had a horrible time" is just a shit thing to say on Boxing Day

Sometime middle of next year "I was thinking about it and Christmas just got a bit too much for me last year, this year I might stay in a hotel near you/stay at home as that will work better for me" - fine, honest but kind and managing your own feelings