You can have handling experience however you MUST be in control of your animal so for individual handling experience smaller snakes are better than bigger ones.
One thing you want is have the parent sign a waiver understanding the possible risks and necessity to properly wash hands before and after the event.
When handling a small snake depending on the age of the child you need to help with the support of the body and should ALWAYS be in control of the head of the animal, the animal's head should be turned towards you never toward the child (so you may need to re-adjust as it goes)
For large animals same principal have the children sitting or standing and have 2 to 3 people supporting the body of the animal and again one person in control of the head.
Know your animals, be able to read them and know when enough is enough, bring more than one so you can switch in between.
I think the personal hands on interaction is important too but it must be done by someone knowledgeable that know's the risk and knows how to avoid them and the key is that YOU have control.