if we are talking about restraints, I vaguely remember going on a rapids ride which featured lap belts of the same type found on an aircraft, this may well have been at the American Adventure sometime around the early 1990's late 1980's ( showing my age)
If the tragic accident was a result of standing up, then what can you do to prevent it? You can install restraints belts and so on, but on that type of ride there would be further risks.
Adult supervision? could be an answer, but is it practical? you cant wrap kids up in cotton wool
young people need to go out and explore their world 10 years and above is old enough ( for most) to be able to go round an environment such as a theme park with a group of friends. The Adult supervision aspect would fall down to the Teachers/youth workers/Scout leaders/Guide leaders knowing the young people, and as a result they usually have an idea on those who would not be suitable to go to a theme park, usually as a result of behavior and the maturity/sensibleness of an individual.
If horseplay is an issue then the parks need/must take a hard line on it, no please sit down, you Must sit down, and if anyone causes issues they should be removed from the park
As a youngster i was lucky enough to go to several theme parks including American adventure, thorpe park, alton towers legoland (Denmark - before merlin) Gulivers kingsdom (Matlock) Alton towers Farup sommerland (Denmark) and others, all in the format of go round as a group of friends, with teachers/Leaders being scattered around should we need them, the only key rule being behave, and be back in time for the coach back - which was usually at a ridiculously early time.
Now i find myself as a Scout leader booking Scouts into places such as Alton towers, yes they are allowed out and about in groups mostly unsupervised, and yes, we have stopped a few from attending Alton towers camp however there are a few key differences between then ( when i was a Scout/school kid) and now, instead of sitting in a cafe drinking tea all day, or mooching round the gardens we ( as leaders) are also out and about on all the rides , nothing like starting your day by cleaning your teeth in warm water in the toilet block in the corporate hospitality suite toilet block, then a few laps on Nemesis first thing. and as for the ridiculously early pick up time forcing you out of the park before its shut ( and having to bail out of queues ) the pick up time is a good 45 minutes to an hour after the park has shut - so now the Scouts get what I didnt and thats a full day in the park until it shuts
Below is a sample of a little info sheet the Scouts get
Anyway all being well should be back camping on the lawn at the bottom of towers street with the lake and the old Towers behind me soon
Regardless of the above all of this is posted as a Young girl has lost her life in what appears to be a tragic accident, family, friends, school teachers, and the immediate staff at Drayton mannor that dealt with the accident from the ride ops who witnessed it, to those who pulled her out of the water and gave first aid - hopefully they are all getting the support and respect they deserve at this tragic time. while time may heal, the loss of someone is a sharp pain that never ever goes away.