Calm down and relax! Cornsnakes are one of the best beginner snakes. As a mother, I can understand your concern for your son's safety. I have let my children pet and hold (under supervision...for the SNAKE's safety) my cornsnakes since they were 3-4 years old. Yes, they can be wriggley, but they are NOT yucky to the touch. Their skin is smooth and dry.
Cornsnakes make excellent pets, especially for children that are learning the responsibility of caring for a pet. Snakes are much more tolerant of not being fed, cleaned, handled, etc on a daily basis. If the child is a few hours...or a few days...late, the snake will be perfectly fine. Forgetting to feed and water the hamster, or to walk the dog can have much more serious consequences. I'm not saying the care of a pet snake can be disregarded, just that a learning mistake or two will be not result in a horrible death of a beloved pet. In addition, the family can go on their week vacation and not have to worry about the snake.
Most cornsnakes rarely bite their owner, and when they do, it is usually because they were being pestered beyond their tolerence while in a sensitive period (such as getting ready to shed) OR it was during feeding time and they were either too eager for dinner and grabbed the first thing they saw or had a case of very poor aim while striking at dinner. I've been bitten by all sized cornsnakes. The little ones just make me laugh. An adult's bite does sting a bit and will bleed, but nowhere near as bad as you might think. My son fell and scraped his knee the other day and it was far worse than any cornsnake bite.
If you do get your son any snake, please research it's proper housing and care before you get the snake. Learn all you can FIRST, set up the viv a week before, and THEN get your snake.