If you are looking for outdoor fun with the kids and a place to have a nice family picnic, Traffic Land (kotsu land) is a good option. Located just outside of the city center in the area called "Oshiba" - which is near Yokogawa and Hakushima areas.
There is a fun go-cart course for kids aged 8 and up to ride solo (listed as grade 3 and up) or ride with an adult (aged 18 or older) in a two-seater. The course is about a kilometer long and you have to follow the rules of traffic as you would on the normal road. Pedestrians walking around the park should also follow the traffic signals,etc. The city government maintains this park as a public safety practice course and many school-kids are brought here on field trips to practice traffic safety.
Alongside the go-cart course, there are a few great picnic areas with grass, shady trees to sit under and a covered Pavillion at the far end of the park if you follow the path through the tunnel and up the stairs.There are also a few playgyms, swings and other playground equipment for little ones to enjoy.
Riding the go-carts only costs 100 yen per lap in a single car or 150 yen per lap in a two-seater. You buy tickets at the vending machine and present it to the staff near the cars.
This traffic-land and park is right next to the Otagawa river. This riverside area is a great loop for traffic-free activity like walks, skating or a jog or cycle without having to worry about traffic. There is also a great cafe not far down the street and a good 24 hour supermarket (YOURS).
Kotsu (traffic) land is located in the Nishi-ku area of Hiroshima city, not too far from the Ushita Astram (monorail) station. It would take around 15 minutes to walk across the bridge to the Kotsu land on the other side of the river from the Ushita Astram stop. Or get there by bus from the Yokogawa train station. Take the #1 buses heading to Kabe and other areas. This bus will pass by the Oshiba-machi bus stop in less than 10 minutes from departure, from here the park is located 250 meters to the east. There is free parking available for 30 cars at a time.