My Mil, diagnosed with mixed vascular dementia and AZ, frequently asks us where the 'little one' is - she also looks for the 'babby' and the 'little girl'. I'm not sure that she can always 'see' these children (and occasionally, the other people that she thinks have been with us - the man, that woman, the little lad) - its more she suddenly asks where they are gone, insisting they were here a few minutes ago, or have been here 'all day', so I am not sure if they are delusions or hallucinations. I do know the more confused she is, the more likely she is to go on about them and often, get upset worrying about them. Sometimes they are my kids (acording to Mil), occasionally hers, sometimes they belong to a neighbour or relative and either she or I have been looking after them. She has got worked up about them to the point, when she is sundowning, that she has accused me (or husband) of doing something 'bad' to one of these missing children - I've grown to dislike any mention of them, as I regard them as an early warning sign of her becomming agitated.
Oddly, at hospital appointments, Mil often claims to see the little girl, usually 'running away' or 'running up and down'. When this happens, then I do think its an hallucination, as she really seems to be able to see this child, as she is speaking.
As to the 'mulitples' (as we call them) - there are often more than one of every person in our house. Mil often talks about the 'other Ann', and the other Ann's husband, who has the same name and looks just like my husband, her son. There are multiples of her 3 grandchildren, and another house that looks exactly like this one, even down to there being a dog there that looks like and has the same name as ours. Often, she wants to know why she is here and wants to go back to her other son (my husband is her only child) and his wife, Ann, and she can get cross, wanting to know why she is being moved round all these houses that look the same. Sometimes, she will ask me a question for the second time in 5 minutes, I'll reply and she will say 'That other Ann told me that too'. She absolutely cannot see anything illogical or strange in there being several people who are not only identical in looks, but who all have the same names as each other - and though she can and will tell you that she only has one son, if you point at him and say 'Thats right - and there he is', she will say that she didn't mean him, she meant the other son. I can pick her up from day care, she will greet me by name - then remark that she thought that Ann was going to pick her up.
Its so hard to deal with, especially when she is getting agitated. I tend to distract and avoid getting engaged in any conversation about these 'other people' or 'missing people', as in her agitation she almost seems to be looking for conflict and anything said directly about them , she can take offence at or try to turn into a row. So its 'Oh - don't worry about that now, how about a nice cup of tea', or similar. I can't say its always successful, but I've found that its the only thing that occasionally works.
I feel for you - its a confusing and stressful thing to deal with