At 7 years old, children should start replacing their first molar or mesial incisors, and the big teeth inside that haven’t been replaced yet will be replaced slowly later. The big teeth inside the mouth are the premolars or second and third molars. The first premolar upper and lower jaw eruption time is generally 10 to 12 years old, the second premolar upper and lower jaw eruption time is 11 to 13 years old; the second molar upper jaw eruption time is generally 12 to 14 years old, the lower jaw 11 to 14 years old, the third molar upper and lower jaw eruption time is 17 to 26 years old. Therefore, the inner big teeth of a 7-week-old child are not yet ready to be replaced, and usually start after the age of 10, so parents do not need to worry. If there is any tooth eruption abnormality, it is recommended to consult a doctor.