My friend works with hiv positive children and is in contact with them without any protection. how long before she catches it?

Will NOT!!: Hiv is not transmitted casually, and contact with people who have HIV disease is quite safe. In order to become infected there must be intimate exchange of body fluids through sex, shared needle use, organ transplantation, blood transfusion, etc. Your friend is doing the children and the community a great service, and thankfully she is not at risk of becoming ill because of it.