[SalesForce] Hide the whole empty row of table in VF page when rendered as pdf

Its not too clear from your question about what problem you are trying to address, but here are two other ways to get the rows from the controller when the page initially loads. (This assumes you are using DataTables.)

1. Normal Visualforce

You can start with a normal apex:pageBlockTable and just add DataTable to it to add the client-side behaviour:

<apex:pageBlockTable value="{!childrenA}" var="c" styleClass="dataTable">
    ...
</apex:pageBlockTable>

<script>
var j$ = jQuery.noConflict();
j$('table.dataTable').dataTable();
</script>

A more detailed example is shown here.

2. Render JSON into the page

You can render the initial JSON into the page by having the controller generate JSON:

public String jsonForChildrenA {
    get {
        return JSON.serializePretty(childrenA);
    }
}

and then assigning it somewhere in the JavaScript in the page:

<script>
...
var jsonForChildrenA = {!jsonForChildrenA};
...
</script>

and then the DataTables fnServerData JavaScript function can just reference that.

I found an easy solution for the problem, no need to implement any logic for the same just included the following attribute -fs-table-paginate: paginate; in tables style tag and worked like a miracle.