没有必要在国内补打疫苗，你只要带上孩子的绿色疫苗本（大部分孩子的疫苗本是中英文都有的），到当地的health department,医生会根据你缺少你的疫苗给孩子补打，然后会给你打印一个有医生签名的Department of Health Certificate of Immunizations，这个证书就是上学孩子需要交给学校的。这个费用并不高，10美元左右一针，有些州甚至是免费的。一般孩子到美国都会买保险，很多保险都会cover这个费用。个人觉得如果在国内补打的话并不合算，因为补打的一般都是自费类。当然每个州可能不一样，你最好看看你还在所在学校的registration information,下面是孩子需要的疫苗。
Vaccinations required for children enrolling in childcare facilities, pre-school, pre-Kindergarten:
Diphtheria-Tetanus-Pertussis (DTaP, or DT if appropriate)
Poliomyelitis (IPV or OPV)
Measles, Mumps, Rubella (1 dose of each, usually given together as MMR)
Varicella (1 dose or history of disease)
Haemophilus influenzae type B (Hib): age younger than 5 years only
Hepatitis B (HBV)
Pneumococcal conjugate vaccine (PCV): age younger than 5 years only
Hepatitis A: 1 dose, required by 18 months of age or older
Children enrolling in Kindergarten:
Diphtheria-Tetanus-Pertussis (DTaP, or DT if appropriate)
Hepatitis B (HBV)
Measles, Mumps, Rubella (2 doses of each, usually given together as MMR)
Poliomyelitis (IPV or OPV): final dose on or after the 4th birthday
Varicella (2 doses or history of disease)
Hepatitis A: total of 2 doses, spaced at least 6 months apart  
All children entering 7th grade (including currently enrolled students):
Tetanus-diphtheria-pertussis booster (“Tdap”): not required if a Td booster dose given less than 5 years before 7th grade entry is recorded on the DTaP/Td  
Verification of immunity to varicella: 2 doses or history of disease
Children who are new enrollees in a TN school in grades other than Kindergarten or 7th:
Diphtheria-Tetanus-Pertussis (DTaP, or DT if appropriate).

打疫苗在美国不需要预约，一般都是walk in, 而且当场给你疫苗记录证明，入学体检的话一般需要预约，大约需等待一周。.