determine height requirements on rides?
The basic determining factors are:
ASTM Standards for amusement rides, which give a range of force tolerances per age or height requirement
Manufacturers and safety restraints, which would be determined by rider proportions, forces, and points of contact
Parks, state laws, and insurance; Factors such as insurance costs, number of back-up or fail-safe systems, type of restraint, and size of the ride may be adjusted at a more direct level, usually in the form of raising the height requirement so that a more mature audience is targeted.
These are the main ones, but there are other smaller factors that are more directed at a park-by-park basis.
i got this off an engineering site, since you dont know the forces placed on the childs body at lower heights or pionts of contact maybe listening to those that do and have calculated these things out would make more sence than ignoring it.