So a guest doesn't follow directions, and he's an idiot, but because the girl is younger, the park is at fault?
8 year olds are capable of following directions, as evidenced by the fact that a teacher is generally capable of instructing 30-odd students for 6 hours or so a day.
If the force of the water was too much and she wasn't able to keep her legs together, the manufacturer needs to revise their designs or their restrictions.
End of the day we're all speculating. None of us have seen video of the incident to know whether the forces caused her to uncross her ankles or whether she just ignored the instructions of the operators.
There's a lot of info surrounding this story that is inflammatory and unlikely, (such as staff not rendering assistance in any way) - Sure, they'll probably get paid somewhat and its likely they'll push for out of court settlement. The big losers here are other guests, as the park will no doubt be required to implement new restrictions on rides such as the age restriction on giant drop, disappointing many, and further reducing the number of attractions any person will go on. It's no longer enough to have your kid measured with a height stick before riding, they now have to be a certain height, weight, age, and come with their own psychiatrist's report stating they're mature enough to handle big red boat.