Depending on the weather, children from kindergarten to elementary school age can splash around safely. With the exception of some deep areas, the deepest part is about chest-high for adults.
There are shallow areas, so even small children can enjoy splashing around. There are many creatures, including river fish, so fishing is also fun.

The water is relatively clean, but not clear enough to be called pure.

There are stairs along the riverside, making it easy to see children playing in the river. There are plenty of trees in the riverside plaza, so shade is readily available.
You can often find families and groups of friends enjoying barbecues in the shade.

[Useful Concerns]

While it is relatively safe, some areas are too deep for adults to reach. Children's safety is important, so supervision is required, including by designating designated areas for splashing around.
While there are toilets, they are not flush toilets and are not particularly clean.