Traveling to Japan with 2 years old child

Hello everyone,

I will be traveling with my parents (70 years old +) and my children (2 year old) to Japan by the end of June for more or less 15 days.

Could anyone recommend me nice tranquil places to visit?

I did already the basic Japan tour few years ago (Tokyo popular places, Yokohama, Kyoto, Hiroshima).

This time I am searching for tranquil and pleasant areas (maybe including country side as well), however, with something interesting to see or do.

Any suggestion? I can rent a car and drive as well, therefore, I am not limited to public transportation only.

I would really appreciate any information input.

Regular weekdays generally tend to be more tranquil than weekends.

Here are some tranquil places that I personally like a lot:

Hokkaido:
http://www.japan-guide.com/list/e1101.html

Hachimantai:
http://www.japan-guide.com/e/e3651.html

Dewa Sanzan:
http://www.japan-guide.com/e/e7900.html

Shirakawago (can be quite crowded during the day, but very tranquil after the departure of daytime tour buses):
http://www.japan-guide.com/e/e5950.html

Kiso Valley:
http://www.japan-guide.com/e/e6075.html

Shibu Onsen and nearby monkeys:
http://www.japan-guide.com/e/e6025.html

Koyasan:
http://www.japan-guide.com/e/e4900.html

Kumano:
http://www.japan-guide.com/e/e4950.html

Overnight stay on Miyajima:
http://www.japan-guide.com/e/e3401.html

Shikoku:
http://www.japan-guide.com/list/e1107.html

Yamanami Highway:
http://www.japan-guide.com/e/e4571.html

Okinawa:
http://www.japan-guide.com/list/e1247.html