Hi Srinivas,
Below is the Visual page and class for your requirement using controller extension. In my example i have used the following objects. You just replace with your objects and fields.You shuld have your parent id in url. Please mark as best answers if it works for you..
Account  - Parent
Opportunity - Child
OpportunityLineItems - Grand child

VP:
<apex:page standardController="Account" extensions="GrandchildDisplay">
    <Apex:pageblock >
    <apex:pageBlockTable value="{!oplist}" var="ol">
        <apex:column value="{!ol.Id}"/>
        <apex:column value="{!ol.name}"/>
        <apex:column value="{!ol.Quantity}"/>
        <apex:column value="{!ol.product2id}"/>
    </apex:pageBlockTable>
    </Apex:pageblock>
</apex:page>


Class:
public class GrandchildDisplay {
    public list<OpportunityLineItem> oplist {set;get;}
    public GrandchildDisplay(apexpages.StandardController std){
         list<opportunity> opp = new list<opportunity>();    
    list<OpportunityLineItem> tempoplist = new list<OpportunityLineItem>();
id accid = apexpages.currentPage().getparameters().get('Id');
    opp =[select id,(select id,name,OpportunityId,Product2Id,Quantity from OpportunityLineItems) oplst from Opportunity where accountid=:Accid];
    system.debug('accountid ' + accid + ' opporty ' +opp);
for(opportunity op:opp)
{
    tempoplist.add(op.OpportunityLineItems);    
}    
    oplist=tempoplist;
    }
}