I understand that it can be upsetting for someone who doesn't visit often to see how much worse someone is since the last time. I do try to warn my sister who lives in the US and can only visit once a year - and my other sister who lives a good 5 hour drive away and comes perhaps once in 3 months. They are bound to notice the changes far more than I do, or my brother, who lives a fairly easy drive away. Our mother doesn't know any of us any more, and shows no recognition when we visit, and if we mention the names of any close family, there is nothing but a blank. My husband does come with me now and then, but she hasn't a clue who he is any more, either. He still tries to engage her in conversation - it is completely one sided and he never gets any response or any sign that she has a clue what he's talking about. But his father also had advanced dementia, so he has seen it all before.
My sister in the US often says she feels bad for not visiting more often, but the fact is that she can't, and I tell her over and over not to feel bad. Even when she does come, sometimes our mother will not even wake up. I know the visits are really more for my sister than for our mother, because whether she's awake or not, and even if she wakes up and is grumpy, she can still kiss her and tell her she loves her, and her conscience will be eased.
You don't say how old your children are, but personally I feel it should be up to them. If they are still happy to go, fine. If they find it upsetting, then maybe it's better for them to remember her as she was.
My two are long grown up and don't live nearby any more, and often say they feel bad for not seeing Granny for quite a while. Again, I tell them not to, since she will not recognise them, and may even be grumpy. My younger was determined to go on the last but one birthday, and went in armed with flowers and a present, and a, Happy Birthday Granny! - only to be met with a grumpy, 'I'm not your granny!' Nowadays she wouldn't even get anything as intelligible as that. But my two are old enough, and have enough understanding of dementia, not to take it personally. They still go now and then, but in the kindest possible way it's more for their own consciences than for their poor old granny now. It would be so lovely if, just once, her eyes could light up when she sees them (or any of us, come to that) but alas, I don't think it's ever going to happen any more. I haven't even told her that our elder is expecting her first baby - our first grandchild - in April. I know I will just get that completely blank look, as if nobody is there any more, and I suppose I would rather keep quiet than have that. All being well, I know that daughter will bring the baby in to see Granny once it's here, and I am still hoping there might be some tiny response to a baby, rather than to mere words. We shall see, but you never know - fingers crossed. At any rate, I know some of the other residents will love to see a new baby.