I've recently discovered a wonderful, child-friendly hike in Kaneohe called Likeke Falls. It's named after the man who created it, the late Richard H. Davis.
It's a very short hike that's nearly all in the shade. It's under an hour round trip if you start at the parking lot of the Ko`olau golf course. The hike ends at the base of the Ko`olau mountains under a 15' waterfall.
I found a website with good directions: http://www.weekendhike.com/2009/07/likeke-waterfall-oahu.html
Olivia and I went up with group put together by a state funded family friendly organization, and we brought lunch to eat at the waterfall.
Along the way I learned about a flower called a rattle shaker (Calathea crotalifera.) Apparently, when the flower dries, the seeds inside make a rattling sound when shaken.
The kids loved splashing their feet in the water, and we all enjoyed the beautiful views of Kaneohe Bay.
Such a pleasant way to start a Saturday morning!