I have four children, have raised six. And ALL but one have gone through a phase of this. Some lasting longer than others.
It's a normal part of growing up,when they were little I paid no mind.
As they got older I never shamed any of them if they were in the family room. Often they didn't realise they were doing it. But I would say,
"I don't mind if you want to Do that but would you mind going to your room please.It's not something everyone needs to see."

Always kept it light or sometimes jokey.
It's really important to remember this is not sexual to children.
Only adults see this as sexual and become uncomfortable.
I am sorry you feel so distraught, please try and allow yourself some understanding.
Take care.