Hi Sandra!!
Def talk to her and tell her right now without your supervision you do not want her to take the kids down there. I'm sure she will understand..
Maybe you (if you want) can bring the kids around Lou'e so you can show them how to behave...2 is my neices age, and around Peanut she doesnt listen to me, so I have to watch her like a hawk when they are around eachother, but the 4 year old you can def teach how to act around a 1 lb Yorkie.
Of course I would wait a little till he gets more shots in him.
Some questions were asked that have nothing to do with your orignal question.. so feel free to ignore those!