I called them yesterday and negotiate salary increase

haven't heard from them yet but it is a 12-month salary rather than 9-month. i contacted my previous department chair when I was a student regarding the salary range and was told what i was offered was kind in the middle. if i get 5k more then will probably toward the high end.
do you know the salary (12-month) for a tenure-track assistant professor at harvard or mit or boston u? i guess it will be field dependent but if anyone can provide a general idea will be helpful.
currently i am holding a tenure-track assistant professor position (for two years). if i move to boston will still at the same level - i hope that the richer research resources at Boston will help.
at the same time, i am a mother with two little ones so i have to consider the living cost education etc and what i can provide for them. it seems that the school system will be better in Boston but the cost for child-care/school is higher...
am i thinking too much? any advices welcome and appreciated.