There are 10 (8?) seats in each vehicle. In our experience, 2 will be a bit wet, 1 will be completely soaked, and the rest will be pretty much dry. There is no way to predict which seat will be which when you get in at loading. The soaked seat usually gets soaked from behind, so it will get his head but it will cascade over his face, not so much splash directly into it.
If it is not hot, I would ride late in the day so you don't walk around wet.
We generally go when it is hot, so we ride first thing then walk around wet (hopefully) so that we stay cool.