I was never dressed as a girl by my mother.
As a kid going through puberty, my mother bought some lacy panties for my younger sister. Until then, she'd worn plain cotton ones, so this was a real departure. The odd thing is that my sister didn't really like them and ended up putting them right at the back of her underwear drawer, never to be worn by her again.
After I first saw them, I had the strange desire to try them on.
I was a latch-key kid and was often home alone after school for about 30 minutes a couple of times a week, so one day I ventured to try on those panties. They fitted me perfectly and they felt fantastic, so it became a regular occurrence.
There was one occasion when I was wearing them and my mother came home earlier than expected. When I heard the front door being unlocked I quickly grabbed my clothes and ran to the bathroom and locked the door. I spent the rest of that day wearing my sister's panties after which I was hooked.