Shikoku or Hiroshima?

I'm planning to visit Japan in August with 2 kids (12 and 14 yrs old). We would like to visit Hiroshima, Matsuyama (Dogo onsen), cycle the Shimano Kaido cycling route (partly starting in Onomichi) and visit the Lya valley. We have 7 days for the above, but need to skip one of the activities/ places above. What would you recommend to visit? We are coming from Nara and need to end in Osaka.

What you skip depends on you. But if you have 7 days for Hiroshima, Matsuyama and Shimanami Kaido, for me (slow traveler) it would seem quite doable.
If I had to skip a place I�fd skip Matsuyama.

One big warning: August is / can be very hot and humid in Japan. I personally can hardly walk outside let alone cycle.
However if that�fs no concern for you and your kids here a summary of my tour of Shimanami Kaido in November 2017:

http://bicycletraveljapan.blogspot.com/2017/11/part-10-day-48-49-ridin...

Enjoy your trip to Japan!

Very handy tips on your blog. Thanks for your response!

It looks doable, but the Iya Valley might be problematic. Are you going to be renting a car? In spite of Shikoku being called a "small island", public transport is quite slow and less convenient. If you have to skip one, that might be the one. You could however easily go to Sandankyo Gorge in Hiroshima.
http://www.visithiroshima.net/plan_your_trip/tour_plans/sandankyo.html
As for Hiroshima itself, there actually is a fair number of places. For the city, there is much more than just the Peace Park & Museum - the Shukkeien Garden and Mitakidera Temple are wonderful and not overrun by tourists.
https://goo.gl/fAz4ax
Presumably, you're also planning to go see Miyajima. If you have the time and energy, you may be able to go see Iwakuni a bit farther down as well.
https://goo.gl/g8HWjh
https://youtu.be/0COOZXi66mM
Sera Kogen might be very nice as well, but I didn't check for August.
http://seranan.jp/fac/seeing/
August is typically sunflower season though, so if interested, there could be something close by to enjoy.
https://www.himawaribatake.net/list_chugoku.php

Are you sure you want to ride a physically demanding trip for 40 km's during the heat of summer with two teenagers???? Just some food for thought....

If you are to visit Shikoku in August, do not miss the Tokushima-awa-odori-festival:
https://japancheapo.com/events/tokushima-awa-odori-festival/

Studying the serious history of Hiroshima would be ideal for your low-teens, so that's something you wouldn't want to change.

But if I were you, I might skip the cycling and enjoy the beaches of the Setouchi islands, because it was recently elected on New York Times as the 7th best place to visit in the world, and summer is an ideal season for your kids to swim at those wave-less beaches!

There are many ferries from either Hiroshima or Matsuyama, which will allow you to make day-trips or stay-overs to an island or two. At many of the islands, you can rent bicycles too, if you're still interested.

The original Dogo Onsen area is a cozy place for sightseeing, souvenir shopping and dining, for all ages, even if you don't use the bath. I've never been to Iya Valley, but it seems nice.

Note that summers have been increasingly hot in the recent years, and on many days during August, the weather forecast warns you to avoid excess activities under the sun.

Here is the link for the NY Times list:
https://www.nytimes.com/interactive/2019/travel/places-to-visit.html