When my SD was 6, her mother would buy her those little kid bras and she wanted to wear them ALL THE TIME. No reason to really, but she wanted to be grown up. I tried to talk her out of them because they usually bunched up under her shirts and she'd be constantly pulling on them because she didn't really need them.
Then at about age 8 she stopped wearing them because they rode up and annoyed her too much.
About age 9 her breast buds started and she was self-conscious about them so I suggested she wear those little cami bras but she DIDN'T WANT TO.
Then at age 10 she really needed a bra or her buds poked out and you could see her nipples through her tee shirts. I bought her some sports bras and some regular bras with a tiny bit of padding to hide the nipples. She didn't want to wear a bra, so she wore baggy tee shirts.
Now she won't go anywhere without a bra, but would DIE if anyone saw her wearing one.
So in a nutshell, she wanted to wear one when she didn't need to, didn't want to wear one when she needed to, and now wears one but doesn't want anyone to know. *sigh*