Education Law Questions? Ask an Education Lawyer
I'm sorry you are being forced to deal with this unpleasant situation. The first thing you need to do is get a copy of the police report against your child, whenever it is made available.
In my opinion the best option, and your next step, would be for you to try to obtain a temporary protective order (a restraining order) against harassment. This would likely be directed at the parent of the child who is engaged in the harassment of your child. This order would prevent these other parties from having contact with you, or your child, to prevent further harassment. In the event the party was to engage in further harassing behavior they would potentially be subject to civil or criminal penalties depending upon the situation. This would prevent the parent from harassing your child, also it would prohibit behavior like what you have described (making false allegations) as that would be considered harassing behavior as well.
Information for obtaining this type of order can usually be found at your local courthouse, or you may be able to find forms online on your local (county or city) governments website.
Once you have applied for the order the court will either grant the order outright, or order a hearing where you will be allowed to explain to the court why this restraining order is necessary for the protection of your child.
Please let me know if I can answer any other questions, or be of further assistance.