Hi Sushil,

Please find below small app where user can select any account from drop down then in child component associated contacts will get display.
Now the requiremnt is i have to update the email id's of multiple contacts at the same time on click oof save button.

AccountParentComponent.cmp

<aura:component controller="AccountContactClass">   
    <aura:handler name="init" action="{!c.doInit}" value="{!this}"/>  
    <table class="slds-table slds-max-medium-table--stacked">
        <th>                               
            <tr>
                <td class="slds-cell-wrap  slds-text-body--large">
                    <b>Account : </b>
                </td>
               
                <td class="slds-cell-wrap">
                    <ui:inputSelect change="{!c.onAccountChange}" aura:id="selectedAccount" >                                      
                        <aura:iteration items="{!v.lstAccounts}" var="account">
                            <ui:inputSelectOption label="{!account.Name}" text="{!account.Id}" />
                        </aura:iteration>
                    </ui:inputSelect>
                </td>
            </tr>
        </th>       
    </table>
   
    <div>                   
        <c:ChildContactComponent/>                                                                                                         
    </div>
</aura:component>
------------------------------------------------------------------------------
AccountParentComponentController.js

({
    doInit : function(component, event, helper) {      
        var selectedAccount = component.find('selectedAccount').get("v.value");
        component.set("v.SelAcc",selectedAccount);
        //Used to get Accounts to show in Drop down
        var action = component.get("c.getLstAccounts");       
        action.setCallback(this,function(a){
            component.set("v.lstAccounts",a.getReturnValue());
        });      
        $A.enqueueAction(action);
    },
   
    onAccountChange : function(component, event, helper){       
        var selectedAccount = component.find('selectedAccount').get("v.value");
        component.set("v.SelAcc",selectedAccount);
       
        var myEvent = $A.get("e.c:accountContactEvent");
        myEvent.setParams({"selectedAccount" : selectedAccount}).fire();
    },
})
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ChildContactComponent.cmp

<aura:component controller="AccountContactClass">
    <link rel="stylesheet" href="/resource/SLDS0101/assets/styles/salesforce-lightning-design-system-vf.css" />
    <link rel="stylesheet" href="/resource/SLDS0101/assets/styles/style.css" />
    <link rel="stylesheet" href="/resource/basicstyle/css/Style2/styles.css" />   
   
    <aura:handler name="init" value="{!this}" action="{!c.doInit}" />
    <aura:handler event="c:accountContactEvent" action="{!c.updateEvent}"/>
   
    <table class="slds-table slds-table--bordered slds-max-medium-table--stacked-horizontal">
        <tr class="slds-text-heading--label">
            <th scope="col">
                <span class="slds-truncate">Name</span>
            </th>
            &nbsp;&nbsp;
            <th scope="col">
                <span class="slds-truncate">Phone</span>
            </th>
            &nbsp;&nbsp;
            <th scope="col">
                <span class="slds-truncate">Email</span>
            </th>
            &nbsp;&nbsp;
            <th scope="col">
                <span class="slds-truncate">Account Name</span>
            </th>
        </tr>
        <tbody>
            <aura:iteration items="{!v.object}" var="obj">
                <tr class="slds-hint-parent">
                    <td data-label="Name">
                        <span class="slds-truncate">
                            <a href="{!'/' + obj.lineId}">
                                <b><ui:outputText value="{!obj.Name}"/></b>
                            </a>
                        </span>
                    </td>
                    &nbsp;
                    &nbsp;
                    <td data-label="Phone" >
                        <span class="slds-truncate">
                            <ui:outputText value="{!obj.Phone}" />
                        </span>
                    </td>
                    &nbsp;
                    &nbsp;
                    <td data-label="Email" >
                        <span class="slds-truncate">
                            <ui:inputText value="{!obj.Email}" />
                        </span>
                    </td>
                    &nbsp;
                    &nbsp;
                    <td data-label="Email" >
                        <span class="slds-truncate">
                            <a href="{!'/' + obj.AccountIDs}">
                                <b><ui:outputText value="{!obj.AccountName}" aura:Id="AccountName"/></b>
                            </a>
                        </span>
                    </td>  
                </tr>
                <tr class="stop"> </tr>
               
            </aura:iteration>
        </tbody>
    </table>
   
    <div>
        <button class="slds-button slds-button--neutral" type="button" onclick="{!c.SaveButton}">
            <span class="slds-truncate">Save</span>
        </button>
    </div>
</aura:component>
-----------------------------------------------------------------------------
ChildContactComponentController.js

({   
    doInit : function(component, event, helper) {      
        var selectedAccount = component.get("v.selectedAccount");
       
        var action = component.get("c.getLstContact");
        action.setParams({
            "accountId" : selectedAccount
        });       
        action.setCallback(this,function(a){
            component.set("v.object",a.getReturnValue());
        });       
        $A.enqueueAction(action);
    },
   
    updateEvent : function(component, event, helper) {
        var selectedAccount = event.getParam("selectedAccount");
       
        var action = component.get("c.getLstContact");
        action.setParams({
            "accountId" : selectedAccount
        });       
        action.setCallback(this,function(a){
            component.set("v.object",a.getReturnValue());
        });       
        $A.enqueueAction(action);
    },
   
    SaveButton : function(component, event, helper) {
        var selectedAccount = component.find("AccountName");      
        var action = component.get("c.getSaveContacts");
        action.setParams({
            "accountName" : selectedAccount[0].get("v.value")
        });       
        action.setCallback(this,function(a){
            component.set("v.object",a.getReturnValue());
        });       
        $A.enqueueAction(action);
    }  
})
--------------------------------------------------------------------------------
AccountContactApp.app

<aura:application >
 <c:AccountParentComponent />
</aura:application>

--------------------------------------------------------------------------------
AccountContactClass.cls

public class AccountContactClass {
 
    @AuraEnabled
    public static List<Account> getLstAccounts() {                      
        return [select id,Name from Account];
    }
   
    @AuraEnabled
    public static List<LineItem> getLstContact(String accountId) {
        List<LineItem> origLineItems = new List<LineItem>();           
        List<Contact> fshList = [select id,Name,Phone,Email,Account.Name,AccountID from contact where AccountID=:accountId];       
        if(fshList !=null){
            for(contact fsh: fshList){ 
                lineItem  li = new LineItem();
                li.lineId = fsh.id;                                                   
                li.Name  = fsh.Name;                               
                li.Phone = fsh.Phone;                
                li.Email = fsh.Email;
                li.AccountName = fsh.Account.Name;
                li.AccountIDs = fsh.AccountID;
                origLineItems.add(li);
            }           
        }
        return origLineItems;
    }
   
    @AuraEnabled
    public static List<LineItem> getSaveContacts(String accountName) {
        List<LineItem> origLineItems = new List<LineItem>();           
        List<Contact> fshList = [select id,Name,Phone,Email,Account.Name,AccountID from contact where Account.Name=:accountName];
        String AccID = fshList[0].AccountID;
        if(fshList !=null){
            for(contact fsh: fshList){ 
                lineItem  li = new LineItem();
                li.lineId = fsh.id;                                                   
                li.Name  = fsh.Name;                               
                li.Phone = fsh.Phone;                
                li.Email = fsh.Email;
                li.AccountName = fsh.Account.Name;
                li.AccountIDs = fsh.AccountID;
                origLineItems.add(li);
            }           
        }

        for (LineItem CU : origLineItems) {
   CU.Save();
  }
       
        return getLstContact(AccID);
    }
   
    public class LineItem{
        @AuraEnabled
        public String lineId {get;set;}
        @AuraEnabled
        public String Name {get;set;}
        @AuraEnabled
        public String Phone {get;set;}
        @AuraEnabled
        public String Email {get;set;}
        @AuraEnabled
        public String AccountName {get;set;}
        @AuraEnabled
        public String AccountIDs {get;set;}
       
        public void Save() {
            Contact c = [SELECT c.Email FROM Contact c WHERE c.ID = :lineId LIMIT 1];
            c.Email = Email;
            update c;
        }
    }
   
}
---------------------------------------------------------------------------------------------

Regards,