Should a 10 year old girl have big breasts?

No, a 10-year-old girl should not have fully developed breasts, as breast development typically begins during puberty, which usually starts between ages 8 and 13. Early breast development can be a sign of precocious puberty, which may require medical evaluation. It's important for children to develop at their own pace, and any significant changes in growth or development should be discussed with a healthcare professional.