Elementary school registration for international students

We are a new MIT family that will be moving to Cambridge in mid-MAY 2012. We have two 7 year old kids and need to find school for them. We search trough the web and found out three very good options, but is necessary to have an address to register. We are in the process of finding in-campus housing but wont have a notice until may. Is there a way we can apply to school in advance? I appreciate if you would share your experiences regarding this process. Than you. ADRIANA.