This is a walk to a waterfall that often isn't much, but it depends on the season. The walk is just lovely, through tropical forest, but it is the most crowded hike on the island, except for Diamond Head, and has some spots where you walk on wet rocks that you have to stretch for.
Children can do this like. Older people, depending on fitness level.
I prefer Lyon Arboretum, just beyond Manoa Falls, lots of tropical jungle trail, parrots overhead, also a walk to a waterfall, probably not very watery, available. It is lovely, very large, and uncrowded. You could do both.