If you are asking what happens to the woman that miscarries (needing a DNC) but was unaware she was pregnant; the answer is simple. The fact that she didn't realize she was pregnant is really moot, because whether she knew or not, a miscarriage happens for a reason. In general, regardless of her knowledge of the pregnancy, she would have miscarried anyway. As far as what happens? If the woman has miscarried, a DNC (more properly 'D&C', from the technical terms "dilation and curettage") is performed to insure the inner lining of the uterus is free of any residual tissue. If left untreated, or without the DNC, infection can set in, in addition to the terrible cramps this woman will experience from the body's natural process of trying to slough off the tissue, which is the cause of cramping. Also, in the event the tissue tears abnormally, into the uterine wall, hemorrhage could erupt. Which left untreated could be fatal. I'm not a doctor, but I've been there, many years ago. Many of the herbs used to cause a miscarriage can also be used to complete a miscarriage and avoid unnecessary surgery that may traumatize the uterus. A D&C can increase the risk of future miscarriages, so many women having fertility difficulties may prefer to use herbs as the most appropriate initial treatment after miscarriage.
Before reaching for an exotic diagnosis, I'd say that yes -- he's being a two year old. When you think about what goes into making even that simple a cause-and-effect correlation, it's not surprising a 2 year old would have some troulble with it at first. How many times in our adult lives do we meet with a stimulus/response pair, and not reailze it? You can help with this. If you can establish a warning that you give -- one the child will always recognize as a warning (so it sounds the same every time), and you find a way to associate this with pain (NOT by inducing the pain yourself of course! This obviously sends the wrong message), you can use this technique as a sort of general warning. The tricks here are (a) always make it sounds or appear the exact same way and, (b) try not to attach an emotional weight to your method of delivery (e.g. don't Scream it or deliver this warning in a way where you sound stressed -- and yes I know it's hard).