Can anything be done about the non-custodial parent violating the supervised visitation order?

the visits, which are now over nights every other weekend, are to be supervised by the non-custodial parents mother. we have received verification that she was not present at all times during the visit. he has filed for joint custody and we have court on may 21, 2013. he is a registered sex offender and we are trying our hardest to keep him out of our sons life. please help.