Is that supposed to be some big deal or something? 12 year old girls typically have no boobs.
Being a boy you should wear a tee shirt instead of a girls bikini top out in public like that.
I had something similar happen to me one time, except my friends did it to me. I was on one of those roller coasters where you stood up and were strapped in, and I jumped in front of my friends in line to get on first. There wasn't enough seats for everyone, so I was the last one to get in, which pissed off my friends. To get back at me, just as the ride was about to take off, my buddies pulled my pants and underwear down, leaving me completely exposed. The coaster rolled out and I couldn't unhook myself to pull my pants up or I'd fall off and get hurt, so I just rode it out and waited, but while riding, the most horrible thing that could happen did: my pants came off, leaving me with no chance of getting them back on! When the ride was over, I covered myself as best I could and told the workers what happened, they laughed at my expense, and sent a worker out to look for them while another worker gave me a towel to wrap around myself.