Having viewed the video several times, it certainly appears that the female may have been texting as the stroller was rolling off that platform and on to the tracks .. she was facing the stroller at the time and had a VERY delayed reaction - way to go MOM !!
I'm not sure what she was doing but she was clearly distracted. We probably already have some Washington types saying we need a new law that requires folks to stay focused when a child is in their care while on a subway/train platform. Stay tuned.
I think they should outlaw cell phones. They are causing more tragedies than guns. Besides that, drug dealers use them and bombs can be detonated with them. Of course maybe they could be kept in a cell phone safe or only allowed to be carried by those with a concealed cell phone permit.