When was the first time a girl saw your penis/erection?

Because since I was just a baby till I was around 10 years old I was usually let to go "au naturel" on beaches, there were plenty of girls from all ages who I'm pretty shure that at one moment they noticed my erected penis, at least that girls who was always "intrested" to give some help while I was digging a hole or while I was building a sand castle...