It's possible. My 6 year old has little boobies, she's not flat chested. And she's a skinny child. Some girls stay flat chested until puberty, others grow breasts slowly, others bloom altogether early. Although the last is usually an indication of excessive weight. So the only reason you should be concerned is if she is overweight, which can cause early puberty. If her weight is normal, then it's just the way she's developing.