A Danish mother did that in New York: http://www.nytimes.com/1997/05/14/nyregion/toddler-left-outs...
Being a Dane myself I can't help smiling when seeing the parent story. I've got a 15 month old daughter, and throughout her entire life she's slept outside for daytime naps. Besides the random playing kid making too much noise, it's been completely uneventful. As a bonus, it means that you've got 1-2 hours of lovely silence indoors before hell breaks loose again...