My 17 month old has started laughing and hitting himself in his dick over and over. I first noticed when l walked in on my mom giving him a bath. She was singing a song about clapping but he was instead hitting his penis and giggling. I told her that he had to be taught to do that... She just thought it was funny. Maybe this is normal behaviour but I'm a ftm so idk. Also l noticed he gets erect at times. Is that normal?