What you do is file for a Modification of Child Support ASAP; you will probably also want to file for a Waiver of Fees and Service.
While the Admin Review Jim described is nice because it doesn't cost anything if it's been more than two years since CS was last reveiewed or modified...it can take a couple of months JUST to get the paperwork processesed and then there is Process of Service and in the meantime, that money is still owed.
If you file in the courts and have Mom servered immediately, then when you go to court, they can backdate the arrearages.
You should be able to get the forms at the local courthouse or possibly online...if you need any help, click on my name and email me.
Second...you mentioned that the police moved him and they shouldn't. I would recommend that you get in contact with a Personal Injury attorney JUST in case.