I am going with 2 kids to Japan in late September, traveling on JR pass Tokyo - Kyoto - Osaka - Himeji - Osaka and back to Tokyo.

Should I book all the train seats ahead of time? Or show up at the station 1/2 hour ahead of time and book seats then?

Booking ahead of time will save time lining up at the station, and ensure we get seats at the times we want.

But booking at the last minute gives us more flexibility and less pressure trying to meet deadlines to get to the station on time.

Considering how fully booked the trains are (I am not sure how full the trains will be), and considering how long you have to line up to reserve seats on a train (I am not sure how long this is), would it be smarter to reserve seats ahead of time or reserve just before each train trip?