The rattling of the tail is just a startle defense, meaning that your snake was just startled by the sudden removal of her hiding place. Explain to your girls that it would be like a giant suddenly ripping the roof off of your house & reaching in at you. Even though your snake knows & remembers that you won't hurt it, it still scares the living daylights out of them!
The only time you'd need to worry is if she coils back to strike, even after giving her a moment to realize that it's you. Hubby will put his hand down in front of them (slowly) after he removes their hide and lets them sniff that it's him before removing them from their enclosure (I'm a bit more unceremonious about it, since I know that their teeth don't hurt, even if they do bite.) Admittedly, his technique makes for a calmer snake, but when I have a hundred cages to clean in just a couple of hours, I have to kind of ignore their feelings for a few minutes. (I'm so mean...just ask my kids!)
I'm only more cautious when I know I have a nervous one that I'm about to pull out. After all, you don't WANT them to get into the habit of biting!
Just remember that cornsnakes' teeth are very small, and even if they do break the skin, it will not hurt. Their teeth are intended to grab, hold & direct prey down their throat, but not to kill or even injure. (They are constrictors.) You have to be more concerned about hurting the snake in your defensive recoil from the strike than them hurting you. I equate a cornsnake bite with getting poked by velcro...yeah, it's annoying & you can feel it, but not really painful. I'd rather be bit by a thousand cornsnakes at once than by a single small dog! (Or scratched by an angry cat!)
The first time I got bit by one of our corns (feeding response, I'd been handling rodents right before), I didn't even feel it! Just looked down & there she was, hanging off of my finger. I was just like, "Huh...so THAT'S what it feels like!" :lol: She immediately let go when she realized that I wasn't food.
Anywho, I hope that puts you a bit more at ease. There definitely is NO better snake for a kid to have than a corn, and I give you crazy mad props for allowing your children to explore their curiousity, even though you aren't as thrilled about their choice of pet! :clap: