As you can see from the comments on this forum people with young children do keep corn snakes, and they are generally agreed to be the best pet snake for children as they are mostly gentle and not too large (about 4 feet). However, it would never be a good idea to let a very small child handle a snake without supervision; even a very tame snake can bite if it is being roughly treated (something highly likely with a small child) and although they aren't a venomous snake you still don't want your child to get bitten, especially as they have quite high salmonella levels. Also, a child too young to handle an animal correctly could easily damage a snake or drop it.
So a corn snake can make a great family pet, but you should never leave your children alone with one until they have learned to handle it and the snake is used to people.
You can find a lot of useful information on this and other points here.