Among all the answers, this is the most accurate one. I tried to help my niece to apply for the ID a few years ago but rejected. According to the immigration, if the child was born after 97, he/she could only get the HKID if & when his/his parents (who has "3-star" on their HKID) come back and stay in HK with the kid. then the kid can get the "3-star" HKID after 7 years.