"Most of the time parents who do this have no choice as they have to work.
Likewise, most parents who don't cook great meals regularly are often too busy."

Mmm, my take on that is quite different. In the Seventies I grew up on a crumby council housing estate where there were a number of single parent families - including mine. My Mum made appropriate efforts to feed me simple but healthy food, while some Mums would just lock the front door and leave the kids out all day while they were really busy smoking fags and gassing to their mates. They got let in at the end of the day for a plate of chips. I still have family on council estates in similar areas to those I was raised, and the situation is now more extreme because that culture of apathy now reigns far more strongly among the working-classes than it did prior to the Eighties.