Locked room for breakables when grandkids stay?

Put not out!

The most precious things in my life are my family, and my relationship with them.

Stuff I want to look after, I put away when they were small. It has come out now they are adults.

We are all entirely relaxed in each others company - no stress.

Well, I don't know about grandchildren breaking things but we have a largish display cabinet which is full of china, not valuable but much of sentimental value.

My namesake (a baby one) just flew in through the patio door, avoided being caught and scuttled behind the cabinet. All has gone quiet. I've left a trail of seed and hope it comes out again but otherwise we're going to have to empty the cabinet and move it to find the little bird.
We're waiting patiently to see if it comes out.

Just put things up higher then the children can reach.
Keep an eye out, and as Visgirl says, take anything they shouldnt have away.

If you have some things which are not so valuable or breakable you could tell them they are allowed to play with those but not Granny's very special ornaments. That way, it will not all seem out of bounds and so tempting.
My granddaughters used to love playing with the Russian dolls, taking them apart, lining them up and putting them back together.

Ours too, though we have one of 24 which is quite difficult to put back together.

Are these breakable items small enough to be put on high shelves or in a lockable cupboard , or are they things like furniture that can be damaged or even pulled over onto small children? I would store moveable items in my own bedroom for the interim, or is the three year old destructive and won't obey instructions?

I would lock the room while the children are too young to be responsible for taking care about what they touch. Any breakages would not really be the fault of a little one. You, and they, will be much more relaxed. If you wanted to show them something precious, you could hold it and let them look but not touch except very gently. That would help them learn that gentleness can apply to things as well as people.

I actually remember vividly being entranced with my gran's china cabinet as a child. She was very poor for most of her life and the things in the cabinet were all gifts from family plus one very small china doll thing that had belonged to the aunt that brought her up. Sadly I broke it when I decided to look at things myself. Usually my gran would take things out one by one to show me them but this day no-one was around. I knew I shouldn't have done it and I was devastated. My gran was lovely about it but I got my backside well and truly tanned by my mother.

It's all very well teaching children not to touch but I would teach them on things that are not precious, until they are old enough to understand. Pack up the bits that really mean a lot and leave the rest until they are older.

When I looked after a godson once a week from he was four months until he was one, I put a hook high up on my bedroom door, and the loop on the door frame, as I had my sewing machine, and all my dressmaking paraphenalia in that room. The door was sufficiently ajar for the cat to go in there is she so desired.(She didn't as she was the kind of female cat with a Nanny-gene.) But there was no way, the child could open the door and get in there.

I also put a chain and padlock on the outer doors of a porcelain stove that was in use during the winter, so he could not open the doors into the actual fire, and kept the kitchen locked when he and I were in the sitting-room, as I knew full well how fast he could crawl.

It is far pleasanter both for the children, their parents and their grandparents if you have removed dangerous or fragile things to a safe place and locked the cupboard or room, than going around saying no and don't dear, for the duration of their visit.

We never had anything too valuable or breakable to fret over.

As others have said, put your treasures high up or hide them in boxes somewhere. Don't lock the children out.

I can remember visiting some elderly well off people who had an incredible collection of dressed dolls, with porcelain heads.

My sister and I, aged about 8 to 10, were invited to look at them but not touch. Literally just that!
I've never been so disappointed in my life 😔