Hello, 

Not sure if I got it right but if you are looking for a clone button that clones the parent and its children you can try the approach bellow.

First of all, you have to create a class with a webservice method that will be invoked by a custom button in the parent's object layout that will clone the parent and its children:
 
 

/**
* @description Helper class to clone parent and its children sObjects
*/
global without sharing class EnhancedCloneHelper {
       
    /**
    * @description Clone parent and its children
    * @param id of the parent sObject
    * @return String Serialized result
    */
    webservice static String clone (String sObjectId) {
        
        List<ParentSObject__c> parentSObjects;
        ParentSObject__c parent;
        CloneModel cloneModelResult = new CloneModel();
        
		// Parent query
        String query = String.format(
            'SELECT {0} FROM {1} WHERE Id = \'\'{2}\'\'',
            new String[] {
                String.join(
                    new List<String>(
                        ParentSObject__c.SObjectType.getDescribe().fields.getMap().keySet()
                    ),
                    ','
                ),
                String.valueOf(ParentSObject__c.SObjectType),
                sObjectId
           }
        );

        try {
            
            // Query and gets results
            parentSObjects = Database.query(query);         
            
			// Clone the original object. Here you can change anything without affecting the original sObject
            parent = parentSObjects[0].clone(false, true, false, false);
            parent.Name = parent.Name + ' CLONED';

            Database.insert(parent);
       
        } catch (DmlException error) {
            cloneModelResult.message = 'An error occurred while cloning the object.' + error.getMessage();
            return JSON.serialize(cloneModelResult);        
        }
        
        // Children query  
        query = String.format(
            'SELECT {0} FROM {1} WHERE ParentSObjectId__c = \'\'{2}\'\'',
            new String[] {
                String.join(
                    new List<String>(
                        ChildSObject__c.SObjectType.getDescribe().fields.getMap().keySet()
                    ),
                    ','
                ),
                String.valueOf(ChildSObject__c.SObjectType),
                sObjectId
           }
        );
        
        List<ChildSObject__c> children = new List<ChildSObject__c>();
        
        try {
            
            // Query and clone the children. Here you can change anything without affecting the original sObject
            for (ChildSObject__c child:(List<ChildSObject__c>)Database.query(query)) {
                children.add(child.clone(false,true,false,false));
            }
            
            // If there isn't any children ends the process and return success
            if (children.isEmpty()) {
                cloneModelResult.isSuccess = true;
                cloneModelResult.message = 'Object successfully cloned!';                
                cloneModelResult.url = getUrlRedirect(parent.Id);
                return JSON.serialize(cloneModelResult);
            }
            
			// Set the parent's Id
            for (ChildSObject__c child : children) {
                child.ParentSObjectId__c = parent.Id;
            }
        
            Database.insert(children);
    
            
        }  catch(DMLException error) {
            cloneModelResult.message = 'An error occurred while cloning the object.' + error.getMessage();;
            return JSON.serialize(cloneModelResult); 
        }
        
        // Return success at the end of the process
        cloneModelResult.isSuccess = true;
        cloneModelResult.message = 'Object and its children successfully cloned!';
        cloneModelResult.url = getUrlRedirect(parent.Id);
        
        return JSON.serialize(cloneModelResult);

    }

    private static String getUrlRedirect(String sObjectId){
        PageReference page = new PageReference('/'+ sObjectId);
        return page.getUrl();
    }
    
    global class CloneModel {
        Boolean isSuccess;
        String message;
        String url;
    }
}

After that, you will have to create a custom javascript button and place it at the parent's layout. Once clicked, the button will invoke the clone method and will clone the desired sObject.




Button's code:
 

{!REQUIRESCRIPT("/soap/ajax/30.0/connection.js")} 
{!REQUIRESCRIPT("/soap/ajax/30.0/apex.js")}

var clonedSobjectResult = JSON.parse(sforce.apex.execute("EnhancedCloneHelper","clone", { sObjectId : "{!ParentSObject__c.Id}" }));

alert(clonedSobjectResult.message);

if(clonedSobjectResult.isSuccess){
  window.location = clonedSobjectResult.url;
}

This is one way to achieve what you are looking for. Keep in mind that you can change it as much as you want.

Hope to have helped. Regards.

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