Children taking inappropriate pictures

My 8 and 5 year old sons have vtech tablets with no internet access or apps that aren’t child friendly. It has a camera but again, none of this can be shared. Other than these tablets my children have no access to electronics. My 5 year olds started running really slow so I was going through his old videos to delete some in hopes to improve it and on it I found a video of the tablet placed on the ground and both boys whipping out their penises and showing it to the camera. This video was taken April 1st. I haven’t spoken to them about this because I don’t want to get angry, since I don’t want to close the door to conversations about these things as they get older but I need some help with how to speak with them about this. Obviously the conversation of private parts are private needs to happen again and I know to some degree this is relatively normal child behaviour. Genuine advice would be appreciated.

@amanda thank you! I think we will just tell them that if we catch this again then they will be grounded off their tablets and they will have to play them in the family room where they can be watched. I don’t want to shame them, my husband and I have agreed that we will just have a quick conversation about how videoing private parts is not appropriate and if they want to explore their bodies they need to do that when they’re alone.