Please help me in displaying parent and child rows in a single datagrid view?

You select data from two tables in two DataTable objects and add both tables to a DataSet object and create a Parent-Child relation using DataRelation object. It a column name from Parent table, and a column name from Child table. After that, you add DataRelation to DataSet.Relations.

If you select data from two tables into a DataSet, do something like this: 

// Create a DataRelation to link the two tables
// based on the SupplierID.
DataColumn parentColumn = dataSet.Tables["Suppliers"].Columns["SupplierID"];
DataColumn childColumn =  dataSet.Tables["Products"].Columns["SupplierID"];
DataRelation relation = new System.Data.DataRelation("SuppliersProducts",  parentColumn, childColumn);
dataSet.Relations.Add(relation);

Now if you bind this dataSet to a DataGrid, you will see PLUS sign and expanding it will show the relations and data related to that.