To me, retired = not working, and don't need to work. If you're not working but you need to work for money...you're unemployed. If you're working but don't need the money, you're not retired. It's possible to retire for a bit, come out of retirement to do something that interests you, retire again, etc.
MMM wishes to redefine the definition of retirement. I disagree, I don't think we need to redefine the definition of retirement; though a whole new word to describe his version of retirement would be fine. It's just semantics though, I'm not going to argue until I'm blue in the face that he's wrong (plus I realize that the meaning of words can change over time).
Anyways....
Are you financially independent? If so, I wouldn't have a problem if you called yourself retired. You're retired from working a regular 9-5 job for a paycheck. Perhaps a bit of wordplay, instead of saying retired, you could say "I'm retired from ACME corporation, so I can be a stay at home parent to my wonderful kid(s)." That should get the point across clearly.
If you're not financially independent, I wouldn't say you're retired, even if you're not planning on going back to a paying job. Yes, it's possible for your spouse to still be working and for you to be retired...but the key (for me) is that your spouse does not HAVE to work; if he/she chooses to, but you are both FI without ever working again...then whoever isn't working can claim to be retired.
That's just me. You'll find many varying definitions of retirement, from "still working to fund his lifestyle" to "bunch of lazy geezers" and all points in between.