Parent field update with all related childs in salesforce

Trigger :

trigger answerOptionManagement on Employees__c (before update) {
    Set<Id> setIDS = new Set<Id>();
    List<Employees__c> listIDS = new List<Employees__c>();
    for(Employees__c  emp : trigger.new){
        setIDS.add(emp.Id);
        listIDS.add(emp);
    }
    if(!listIDS.isEmpty() && listIDS.size()>0){
        cmdMainOperation(listIDS,setIDS);
    }
    public static void cmdMainOperation(List<Employees__c> listIDS,Set<Id> setIDS){
        AggregateResult [] aggr = [select count(id),First_Name__c fristName,Employees__c employeeId from Contact_Us__c where Employees__c IN :setIDS and First_Name__c != null group by First_Name__c,Employees__c  order by First_Name__c desc];
        system.debug(aggr);
        Map<Id,String> mapAggr = new Map<Id,String>();
        for(AggregateResult agr : aggr){           
            system.debug(mapAggr);
            string category=String.valueOf(agr.get('fristName'));
            category = category.subString(category.indexOf(':')+1,category.length());
            if(mapAggr.containsKey(String.valueOf(agr.get('employeeId')))){
                String strCategory = mapAggr.get(String.valueOf(agr.get('employeeId')))+ ','+category;
                mapAggr.put(String.valueOf(agr.get('employeeId')),strCategory );
                system.debug('mapAggr in if 21 line--->>'+mapAggr);
            }else{
                mapAggr.put(String.valueOf(agr.get('employeeId')),category);
                system.debug('mapAggr in if 24 line--->>'+mapAggr);
            }
        }
        for(Employees__c emp : listIDS){
            if(mapAggr.containsKey(emp.id)){
                emp.Answer_Options__c = mapAggr.get(emp.id);
                system.debug('emp.Answer_Options__c in if 30 line--->>'+emp.Answer_Options__c);
            }
           
        }
       
    }

}