Hi Kerri,
Thanks so much for your sweet words about the Moms Panel! We sure love helping guests plan the most Magical vacation possible.
Now, about these two fantastic rides...my children all rode both of them as soon as they were tall enough. Like you, I'm a proud safety nerd. My 9 year old still uses a booster seat in the car (just don't tell her friends). I have always felt completely safe on all Disney attractions, and I'm a thrill ride fan so I've ridden them all.
Soarin' is such a cool attraction! The thing is, while your "hang glider" does lift off the ground, you don't really go anywhere. It's a motion simulator so you feel like you are soarin' above California as you watch the movie screen in front of you. This amazing attraction has seat belts and smaller aviators also have a center strap that comes up between their legs and you thread the regular seat belt through that loop for extra security. There is a "minimum height line" on the seats and if someone is shorter than that line, they have to use the center strap.
Kali River Rapids is another awesome ride. My youngest rode it at 4 years old, as soon as she was tall enough. There are seat belts on this attraction as well. In addition, there's an extra bar that comes across in front of little ones for an extra safety measure. This ride is a blast, especially when someone you know gets soaked.
Hope this helps and have a wonderful time,
Kaylene