For $230 net possible reimbursement from insurance, and guaranteed increase in premiums (and possibly cnacellation since arson by a renter), I certainly would not go with your insurance route - however, failing to report it could also cause them to cancel you, so tough decision. However, your insurance should not be covering this.
You should file a claim against THEIR renters insurance policy for coverage of the loss, though you could probably also take it out of their damage deposit and require they pay the remaining amount (directly or out of their insurance), PLUS refill the deposit - you would have to check state/local laws on whether you can use their depsoit in this way.
Your other decision is whether to evict them for their kid's arson - if you fail to, could cause major liability issues for you, lose you the property insurance, and incredible liability for you if this is a multi-family property.
Personally, I think you need to talk to an attorney on your options (cost may be recoverable from them too as collection cost as part of the damages depending on law in your area and your lease agreement). I think your first step is a registered letter to them demanding reimbursement for the damages - how they come up with it is their problem, out of pocket or insurance - then address the eviction issue with your attorney.