I think it depends on your family. It does get muddy and sometimes a bit slick from the mud, but I hiked this with my kids, 7 and 9, as well as my sister and her kids, 4 and 1.5. She kept the little one in his ergo and the 4 year old walked. We took it slow and had fun but did end up pretty muddy and had rain pour down on us at one point. I would bring towels and a change of shoes at the least.
If you want an easier waterfall hike, you could look at Waimea falls, which is all paved and has botanical gardens, it would be much cleaner but of course a different type of experience