Not the parent, but I've still got a MBP adapter that has to be at least seven years old, and it still get regular use. Out of the four or five MBP/Airs between the wife and I, we've never had a power adapter go bad. We also don't have contests to see who can wrap the wires of the adapter the tightest with the tightest loops, so that might have some bearing on our results.
FWIW, I don't recall ever having to replace a modern-style Mac power adapter. I had one of the early first generation Magsafe ones fail, but the later ones of those have lasted years, and so far all of the second-generation (thin) Magsafe ones are fine too. Pre-magsafe I went through a lot.
Just one. I'm always very careful with it. The cable was still intact. One of the common problems many people have is with breaking cable, especially at the end of the adapter. I always make sure it has enough space.