I think it's common for children and siblings to be curious and experiment or play games like "show and tell" to each other. As a child, your sibling is likely your best friend and someone you can trust and tell anything to. As for actually "play hum ping" or lap dancing....not so sure about that.
I had to lap dance a girl in a dare....I didnt know her....and then....then.............she licked me :S
I... think. If I understand what you are talking about.