Hi,
If you are looking for international schools in Tokyo, check this list
International Schools List | Useful Information | realestate-tokyo.com
I would recommend ASIJ (American School In Japan, Nishimachi or Yokohama purely on their reputation). You need to be a little careful as some schools use ththe name 'international' when they are really not fulfilling all the criteria - i.e. do the exams your children sit meet accreditation requirements in your home country?