All Softshells tend to be extremely bitey and scratchy. They obviously lack the main defense other turtles have (the hard shell), so immediately resort to trying to tear you to shreds when threatened.
As a pet for your son, I wouldn't say it was a wise idea (althought that would depend on the age of your son). These turtles are fascinating, but bite hard (my Chinese Softshell at 3" long, can draw blood and take a chunk out of my finger) and there isn't an easy way of handling them even to remove them from the tank for maintenance.
With Sliders, you can hold the back of the shell, between the hind legs, and you're safe from bites and scratches. Softshells have incredibly long necks, that can perform exorcist-style turns, and bite you even when this holding technique is employed.
Cute, but not an easily maintained turtle.
Paul