But there are PLENTY of examples of log flumes operating at theme parks around the country with drops larger than 50 feet with no lap bars (many of which have even shorter height requirements). As an example from one of my favorite amusement parks (outside of Orlando), Knoebels log flume has a 55 foot drop with no lapbars and a minimum height requirement of 36" (with an adult). (
http://www.knoebels.com/rides/giant-flume). Now it might be possible that the expectation is that an adult would be holding/restraining anyone under 42" (the minimum height to ride alone) as the seats are toboggan style, but still...
On a side note, by nearly 3 year old daughter is just over 36" now and has ridden a couple log flumes already. We have just over a year until our Disney trip for her to grow about 4 inches, otherwise I know she's going to be disappointed to have to miss Splash Mountain, especially after having been able to ride other log flumes (and loving them) previously!