Thanks everyone for your advice. After thinking it through and doing some research we decided that we will enjoy Japan better when the boys are a year or 2 older and also that for the price of the Japan trip we can go to Thailand in march and ski in NZ in July (at Cardrona where they have a great kid's program)and get sand and snow so that's what we're doing
I guess I still haven't become a sensible person - one day.....