I have a ten year old son, and then a 9 year old, 5 year old and 2 year old daughter – would it be yichud to bring a female babysitter?
It is permitted. The reason id since there are two men, and one woman it isn’t yichud by day, and even at night when one of them might be sleeping, there still is the third child of five. Even though a child of five is borderline if he is mature enough to be a shomer, for this we can be lenient, as many poskim say that it is old enough.
Rema E:H 22-5, Dvar Halacha 4-2,Shevet Halevi 5- siman 204 -1,Toras Hayichud 8-5, NIti Gavriel 29-3.