vb2005 datagrid records editing locked with the priviledge to edit only newly added r

I am using vb 2005 with MSAccess. I am having one data entry form with datagridview showing child table records.Now I want that the user can add new record, edit that newly added record and delete that also but can not edit the existing records nor delete them.
How can I achieve this ? I am searching for the help for last 3-4 months but could not find one.