Serious Hard Times

I'll try outlining my opinion about this legal case here, but take note that I'm not a lawyer and I don't even live in America, so my assumptions are based on German law and might not apply in the USA.
The pool is surrounded with attention signs, this means that everyone is expected to read the signs and at accordingly. If someone enters the pool, it is a violation of the rules and the aquarium or any employees including you are not responsible for any injuries that might happen as a consequence of breaking the rules. Parents must watch over their children at all times to make sure they don't misbehave, and if something happens to the child as a consequence of entering a restricted area, it is the parents' fault for not watching the child. There wasn't even a way for you to react to the child holding its hand into the water in time, so it can't be your fault. If anyone is to be sued over this, which would still be absurd, it is the aquarium as a company because they didn't protect people from the stingrays enough. I can only imagine what would happen if someone fell into the pool. I strongly suggest speaking with your boss or the aquarium administration about this issue and getting their help. They will have better options to defend you in court. And lastly, be confident. Read your contract, read the laws. Write down an argumentation why you are innocent. It would probably not hold up in court, but your lawyer or the aquarium's lawyer can make a rock solid legal argumentation out of it when you present it to them. The US courts are known for being corrupt and broken, but with the support of the aquarium, justice will win. You can't be sued for something you couldn't prevent. Oh, and don't let it get you down. Suicide is the coward's way out. Be bold and fight back! Don't give those snobs satisfaction. Don't give them anything!