I don’t see why you can’t be an extra parent for your son’s group.  THe other parent rides the bus and you and your daughter drive and meet there.  This is ridiculous that they can’t find a solution for this.  I would ask them to chang their "rules" about you going on your own and helping with them.  As they say this is new to them.  When new factors have to be taken into consideration sometimes rules need to be changed. My other thought is just go anyway and give them a cell phone number.  YOu don’t have to be with them the whole time but can be on call.  Good luck  Julia