At that age, I was 5'5," had a paper route, knew how to buy groceries & use the phone, knew the police chief's name, knew well the pastor of my church, could cook, clean, make sure my younger brother was OK, had an aunt and uncle within walking distance. Not saying the Iowa mother was OK by leaving, but it's not the worst of crimes.
I agree with you that 12 year old children are capable of handling a lot of responsibility. I certainly was at that age. Even younger. I was quite capable of feeding myself at 5. However in this current age parents are not even held accountable for feeding their school aged children. At most schools with low income and even middle class students, breakfast is served as well as lunch. Some even send home food for dinner and even provide meals during the summer months. Families receiving food stamp money are not required to spend it on their children. In the end, less is expected of parents and their children because so much is simply provided for them.
You need to remember that these kids are being raised in the 21st century in the United States. This is pretty bad IMO. Not to say she had a stable mind to begin with.