Hello Prakash,

You would have to somehow keep track of whether or not the parent record has been edited. You can potentially do this by using the Record.Tag property. You can simply set it as a Boolean to true for this purpose.

Then you can use the EditModeStarting event to see if the ParentRecord's Tag property is true. If it is then cancel the event:

void grid_EditModeStarting(object sender, EditModeStartingEventArgs e)
{
    bool isParentEdited = (bool)e.Cell.Record.ParentDataRecord.Tag;
    if (e.Cell.Record.FieldLayout.Key == "Child" && isParentEdited)
        e.Cancel = true;
}