If you see these small breast buds, it’s time to get a first bra. Breast buds are small bumps that appear under each nipple.  However, if a girl is feeling self conscious about her breasts, it might be time to get a bra - regardless of physical development.  You should feel some tenderness or soreness when breasts begin to bud. This is normal, and nothing to be concerned about. It just means you are starting to develop.  Next, the nipples and areola (circle of skin around them) will get darker and bigger. Then the breasts will start to grow more, at first perhaps having a pointy shape. The average age for a girl to start wearing a bra is age 11. Some girls need one by age 8, though, and some girls don’t need one until they are 14. Every girl is different!  Sometimes girls who aren’t really that developed ask to wear a bra because their friend is wearing one. They could start out by trying a training bra  You could also start out by wearing a tank top under your shirts. Either way, you should not stress out about whether you are developing like other girls. Everyone moves at their own pace, and that's OK. Developing breast buds is just one of the many changes a girl will see in her body as she starts to enter puberty.  She might start to grow pubic hair. In some girls, pubic hair actually develops before breast buds appear.  Puberty can cause a girl to gain some weight, especially in the belly area. The belly might look more rounded. This is a natural sign that a girl is starting to mature physically. The girl also might start menstruating, although her periods might be very infrequent at first. All of these things are normal signs of puberty.

TL;DR in Vietnamese:
Để ý tới chồi ngực đang nhú ra. Hiểu về độ tuổi dậy thì trung bình của các bé gái. Nhận biết dấu hiệu dậy thì.