To search for possible sons I think you'd need some clues as to Ellen's maiden name and the name of her husband. Flood is quite a common surname so it would be very easy to pick up the trail of the wrong family ... particularly with such early dates where few parishes have records.
I dont believe that counties Kildare and Westmeath have any border - neighbouring counties to Kildare are Dublin, Meath, Offaly, Laois, Carlow & Wicklow
Shane