What should I say to my mom that I want to wear a training bra??!! *GIRLS ONLY!*?

Ok.. So I'm 10 years old and most of my friends wear training bras. I ki da think I need one too. I wear the camis with built I. Ones so would my mom care?! I have been baling trouble with this for a while now and I need a longish smart answer! GIRLS ONLY AWSNER!!!