Okayama Castle originally made in 1597, was destroyed in the last year of WWII and was rebuilt in 1966. Thus, the original castle like Himeji Castle is a better castle. But Okayama Castle is located on the Asahi River, which was used as a moat and the more famous Korakuen Garden is located just across the river. It's easy to go to Kairakuen Garden and Okayama Castle by a bus or a tram from JR Okayama Station. You should also go to Kurashiki, and consider going to Naoshima Island.

It might be too late but・・ Only for the sightseeing of the castle. Over 20 people of children costs 100yen. for adults, 300yen per person. There is English brochure. I hope you have(had) fun.