Not so quick. I would think the kid might just have a little advantage. Correct me if I'm wrong. Not only must he be one strong cookie, he has an advantage on the filed, a kind of stealth one. Runners don't look down normally when you are running, they are looking ahead for a path, and if he's below eye level, whamo!
Now I am not say that the kid with no legs couldn't tackle, I still believe that the kick returner would get an earful from his friends and teammates for "tripping" over the legless player. It would be like losing to a girl or something.