If it's a smaller child or infant, place one on the middle of the chest and on the child's back. (if it is a bigger child with enough room for two, place one on the upper right/your left of the chest, and one on the lower left/your right) the pads should never touch each other.
Knowing if a patient has tuberculosis, hepatitis b, or aids is important because a. serious illnesses should be avoided. b. they could compromise the vital sign readings. c. cross-infection may occur. d. they can't be cured.