Hi,

Try the below code snippet as reference

<apex:page controller="RelatedChildContact" tabStyle="Account">

<script>
function CloseWindow()
{
alert('client');
// window.parent.close();
// OR

var winMain=window.parent.opener;
// alert("window.parent.opener ="+window.parent.opener);
// alert("window.parent.opener.location ="+window.parent.opener.location);
winMain.HelloFromChild();
window.top.close();


}

function CloseWindow2(st)
{
// alert(st);
if(st!='no record selected')
{
// alert('IDs with separator'+st);
window.parent.opener.document.getElementById("str1").value=st;
window.parent.opener.displayContact(st);
window.top.close();

}
else
{

alert('Please select atleast one contact to be displayed');
window.reload();
}

}
function CloseWindow3(st)
{
// alert(st);
if(st!='no record selected')
{
// alert('IDs with separator'+st);
window.parent.opener.displayContact2(st);
window.top.close();

}
else
{

alert('Please select atleast one contact to be displayed');
window.reload();
}

}

function SelectedID(checkedIdd,i)
{

alert('hi'+checkedIdd+'__i'+i);

return false;
}

</script>
<apex:form >

<apex:pageBlock Title="Contacts with CheckBoxes">

<apex:pageBlockSection Title="List of Available Contacts">

<!--<apex:dataTable value="{!Contacts}" var="ct1" columnswidth="50px,50px" cellpadding="4" border="1">-->

<apex:pageBlockTable value="{!Contacts}" var="ct1" columnswidth="50px,50px" cellpadding="4" border="1">
<apex:column >

<apex:facet name="header">

<apex:inputCheckbox >

<apex:actionSupport event="onclick" action="{!GetSelected}" onsubmit="checkAll(this)" rerender="Selected_PBS"/>

</apex:inputCheckbox>

</apex:facet>

<apex:inputCheckbox value="{!ct1.selected}" id="checkedone">

<!-- <apex:actionSupport event="onclick" action="{!GetSelected}" onsubmit="SelectedID('{!ct1.con.id}','{!count}');" rerender="Selected_PBS"/> -->
<apex:actionSupport event="onclick" action="{!GetSelected}" rerender="Selected_PBS"/>
</apex:inputCheckbox></apex:column>

<apex:column headervalue="Contact Firstname" value="{!ct1.con.firstname}" />

<apex:column headervalue="Contact Lastname" value="{!ct1.con.lastname}" />

<apex:column headervalue="Phone" value="{!ct1.con.Phone}" />

<!--</apex:dataTable>-->

</apex:pageBlockTable>
</apex:pageBlockSection>

<!-- /* New Section */ -->

<apex:pageBlockSection Title="Selected Contacts" id="Selected_PBS">

<apex:dataTable value="{!SelectedContacts}" var="c" columnswidth="50px,50px" cellpadding="4" border="1">

<apex:column headervalue="Contact Name" value="{!c.Firstname}" />

<apex:column headervalue="Contact LastName" value="{!c.lastname}" />

<apex:column headervalue="Phone" value="{!c.Phone}" />

<apex:column headervalue="Email" value="{!c.Email}" />

</apex:dataTable>

</apex:pageBlockSection>
</apex:pageBlock>

</apex:form>

<script>

function checkAll(cb)

{
//alert('__cb'+cb);

var inputElem = document.getElementsByTagName("input");

for(var i=0; i<inputElem.length; i++)

{

if(inputElem[i].id.indexOf("checkedone")!=-1)

inputElem[i].checked = cb.checked;

}

}

</script>

</apex:page>
====================Controller================================

public with sharing class RelatedChildContact {

public String param1 { get; set; }

public String str{get;set;}

public RelatedChildContact ()
{
param1=ApexPages.currentPage().getParameters().get('q');
system.debug('____param1'+param1);
}

List<contactwrapper> contactList = new List<contactwrapper>();

public List<contactwrapper> getContacts()

{
contactList.clear();
for(Contact c: [SELECT id,firstname,lastname,email,Phone from contact Limit 10])

contactList.add(new contactwrapper(c));

return contactList;

}

List<Contact> SelectedContacts= new List<Contact>();


public PageReference getSelected()
{


SelectedContacts.clear();

for(contactwrapper conwrapper : contactList )

if(conwrapper.selected == true)
{
SelectedContacts.add(conwrapper.con);

}

return null;

}

public List<Contact> GetSelectedContacts()

{
System.debug('______SelectedContacts.size()'+SelectedContacts.size());
if(SelectedContacts.size()>0)

return SelectedContacts;

else

return null;

}

public void Retrieve()
{
str=null;
System.debug('___R___SelectedContacts.size()'+SelectedContacts.size());
if(SelectedContacts.size()>0)
{
for(Integer i=0;i<SelectedContacts.size();i++)
{
System.debug('__'+i);
if(str==null)
str=SelectedContacts[i].id;
else
{
// if(!(str.contains(SelectedContacts[i].id)))
str=str+'####'+SelectedContacts[i].id;

}
}
}
else
{
str='no record selected';
}
system.debug('______str'+str);
}

public class contactwrapper

{

public Contact con{get; set;}

public Boolean selected {get; set;}

public contactwrapper(Contact ctt)

{

con= ctt;

selected = false;

}

}

}

Did this answer your question? If not, let me know what didn't work, or if so, please mark it solved.