Traveling with kids can be a huge challenge when they're young. Planning activities great for stress release is a great way for your whole family to refresh and get the most enjoyment out of your vacation to Japan.
This is why you need to remember Jinzan Park for when you come to Kochi. In the hills just outside the charming small town of Kami, about a thirty minute trip from downtown Kochi, Jinzan Park is also surrounded by nature.
There are several large parks dotted around Kochi Prefecture, but Jinzan Park is the newest one I've seen that is also near the city. If you don't mind a short walk, it is also accessible by train from Tosayamada Station.
One of the instantly surprising features of the park is, drumroll please--grass! There is even a big hill of grass that you can slide down on a cardboard box or just roll down, if you're feeling brave. There is plenty more grass for sitting around and having a picnic.
The park is big enough for your kids to run around, check out all of the interesting things to do on the jungle gyms, and try out the various types of slides. Since small kids require supervision, you will definitely tire out before they do! There are three different "zones", one for bigger kids, another for 3-6 year olds, and another for toddlers.
I would really recommend a spring or autumn visit as there wasn't much shade. A lot of the trees at the park were still young, and on a hot summer day I can imagine the park being pretty miserable. If you do go in summer, just be sure to get there early!
Also, if you can manage not to go on Sunday, I really recommend it. The park was packed on the day we went, which meant I spent most of the time keeping my daughter from being trampled under the stampede of bigger kids.
Kami is also a very lovely town with a lot of really excellent restaurants and cafes. After you have worn yourselves out at the park, you will then probably want to search out a nice, cool place to relax before heading back to Kochi City.