public class SampleController {

    private ApexPages.StandardController con;
    public Parent2__c parent2 {get;set;}
    public Parent1__c parent1qry {get;set;}
    public List<wrapper1> wrapList1 {get;set;}
    public List<wrapper2> wrapList2 {get;set;}
    public List<Parent2__c> parent2list {get;set;}
    public List<Child2__c> child2list {get;set;}
    public Parent2__c NewParent2 {get;set;}

    public SampleController(ApexPages.StandardController controller) {
        con = controller;

        wrapList1 = new List<wrapper1>();
        parent2 = new Parent2__c();
        parent1 = new Parent1__c();
        parent2list = new List<Parent2__c>();
        child2list = new List<Child2__c>();
    }

    public void init() {

        List<Child1__c> items = new List<Child1__c>();

        List<wrapper1> tempWrap = new List<wrapper1>();

        if(parent2.Parent1__c != null) {
            parent1qry = [SELECT Id, Name, Account__c, Account__r.Name,  Date__c, Total_Amount__c FROM Parent1__c WHERE Id=:parent2.Parent1__c];

            items = [SELECT Id, Parent1__c, Item__c,  Item__r.Name, Quantity__c, Unit_Price__c, Total_Price__c FROM Child1__c WHERE Parent1__c =: parent2.Parent1__c];

        }

        for(Child1__c liloop : items) {
            tempWrap.add(new wrapper1(false,liloop));
        }


        if(tempWrap != null) {
            wrapper1 = tempWrap;
        }
    }

    public PageReference save() {

        List<Parent2__c> ListParent2 = new List<Parent2__c>();
        List<wrapper2> LineItemList = new List<wrapper2>();
        List<Child1__c> litem = new List<Child1__c>();
        Parent2__c NewParent2 = new Parent2__c();

        NewParent2.Date_of_Return__c = parent2.Date_of_Return__c;
        NewParent2.Customer_Name__c = parent1qry.Account__c;


        Set<Id> newIds = new Set<Id>();

        for(wrapper1 wloop : wrapList1) {
            if(wloop.IsSelected) {
                NewParent2.Child1__c = wloop.line.Id;
                if(wloop.line.Parent1__c != null) {
                    NewParent2.Parent1__c = wloop.line.Parent1__c;

                }
                ListParent2.add(NewParent2);
            }
        }

        if(ListParent2.size() > 0) {
            insert ListParent2;

            Set<Id> ids = new Set<Id>();

             for(Parent2__c idloop : ListParent2) {
                ids.add(idloop.Id);

            }

            List<Parent2__c> parent2qry = [SELECT Id, Name, Customer_Name__c, Date_of_Return__c, Parent1__c, Child1__c FROM Parent2__c WHERE ID IN : ids];


            parent2list = parent2qry;


        }

        PageReference pageref = new PageReference('/' + NewParent2.Id);
        pageref.setRedirect(true);
        return pageref;
    }

    public class wrapper1 {
        public Child1__c line {get;set;}
        public Boolean IsSelected {get;set;}

        public wrapper1(Boolean s, Child1__c li) {

            IsSelected = s;
            line = li;

        }

    }

    public class wrapper2 {
        public Child2__c c2 {get;set;}
        public Integer index {get;set;}

    }


}

map<Schema.SObjectField,Schema.SObjectField> fromFldToFldMap =
          new map<Schema.SObjectField,SChema.SObjectField> {
               Child1__c.Foo__c => Child2__c.Foo__c,
               Child1__c.Bar__c => Child2__c.Bar__c,
               ... note Child2 field names don't have to be same as Child1
               .. but types must be same};

Wrapper2[] wrapList2 = new List<Wrapper2>();
for (Wrapper1 w1 : wrapList1) { //copies all Child1s to Child2s
   Wrapper2 w2 = new Wrapper2();
   w2.c2 = new Child2__c(Parent2__c = parent2.Id); // parent of ea Child2
   w2.index = wrap2List.size();
   wrap2List.add(w2);   // add to list of all Child2

   // Copy values from Child1 obj to Child2 obj using our map of source name to target name
   // Relies on SObject class methods get(..) and put(..)
   for (Schema.SObjectField fldToken : fromFldToFldMap.keySet())
       w2.c2.put(fromFldToFldMap.get(fldToken),  // name of fld in Child2
                 w1.line.get(fldToken);        // value (as Object) of corresp fld in Child1
}