Personally I would recommend against doing the same day connection due to

1. What if plane delays
2. What if NEX is shutdown due to wind (it happens)
3. Other reasons as mentioned by others

And while you can get most of the fare covered for taking the overnight train when using JR Pass, unless you or your boys are interested in train, I would rather stay in a proper bed on the night of arrival and take Shinkansen / Domestic Flights that as AlwaysAisle mentioned in the following day, did you also consider flying into KIX first and flying out of HND / NRT?

If your international ticket is from ANA or JAL you can get the domestic tag on relative cheap too (if you haven't ticket it that is).