They had to have learned this from someone or something as I don't believe this is normal. I would strongly suggest having a talk with them and explain how inappropriate their actions were. Also have a talk with the babysitter about leaving them alone and letting this behavior go on. I wouldn't leave them alone together anymore.
the baby sitter was upstairs as was the older cousin. At first we heard that they were just taking pics & of each other & everything around them thought ok curiosity. But when we found out there was more too it then we were concerned.
Um, no this is not normal. A peak, perhaps. But sniffing, licking and taking pictures---- no. That is most likely learned behavior, I hate to say. I'd be very worried. The taking pictures takes it to a whole new level. I'd do my best to get to the bottom of it. (oh, and FIRE that babysitter.!!!!!!!!!!!!)
So where was the babysitter while this was going on ...and pictures ??