No, you cannot sue. You can only sue when someone is negligent; negligence is judged by what a reasonable person *of that age* would do; there is nothing unreasonable for one child to give a nickel to another, and so no negligence..Furthermore, someone is only liable when the harm is foreseeable: it is not foreseeable that your child would swallow a coin, since that is not what you do with coins, if you are child old enough for recess.And you can't sue when you--or in this case, your child--caused the harm, such as by swallowing an inappropriate foreign object.