Just my two exchangable minor currency units, but staying overnight both in Kyoto and Nagoya/Aichi might be a wise thing to do. Kyoto is a city that has hidden wonders in store in very unexpected places and leaves especially younger visitors with unforgettable memories of sights and sounds. Please give your kids the chance to experience the summer sunrise in that ancient Imperial capital, maybe having a breakfast picnic along the Kamo river with sight of the surrounding mountains. I was 19 during my first trip to Kyoto and the memory has never left since...

A full day at the Aichi Expo might also be a winner, especially after reading jpatokal's excellent trip report at: http://www.flyertalk.com/forum/showthread.php?t=419260 I have a tight schedule to attend for lowly business purposes but would love to stay for a whole day or two if possible...