Answer: Going by your decription and the late summer timing, I would make a guess it is Impatiens balsamina, an old fashioned annual, also sometimes called Garden Balsam. If this is the plant, it will eventually form seed pods that sort of explode when touched.
There is a photo of some young plants here
(You may need to cut and paste the url into your browser to make it work correctly.)
Q&A Library Searching Tips