Good advice above. By the sounds of your previous owners, there may be trash in the pond itself. You know that phrase..."out of sight, out of mind". I would be leery of letting kids swim in there till you know that there isn't anything in there that can hurt them/cut them up.
If you are leaning towards expanding the pond, look for some pond guys to get out there to give you quotes. At the same time, they will offer ideas that you may not have thought of.
Welcome to PONDBOSS, you'll learn a lot here!
