My Daughter was 5 when I started getting into ball pythons. She now 9 and since she was 6 she has been keeping Kenyan Sand Boas of her own and they live in tanks in her room. She has been nipped by her kenyan sand boas, we wash the wound (pin pricks basically) with dial and water and she doesn't even need a band-aid. She knows how to wash her hands properly and she does so after she cleans, feeds and handles her snakes or mine. Education is the key. If your child is an infant/toddler I would not let them hold the snakes but I would say from the time you can teach them to be gentle holding the snake with supervision shouldn't be a problem at all. Just make sure that you wash your kids hands after touching the snake.
For the snake killing the child fear it is really unfounded. If you are on here you should know how to keep your snake in a proper enclosure which prevents escapes. Even in the event of an escape I just can't see the snake seeking out the child to hurt it. Honestly snakes in general are safer than pretty much any other household pet (as people have already stated.).