From the article:
Married women with kids who lost their jobs between 2007 and 2009 had a 31% lower chance of finding a new job than married fathers with kids. But their alter-egos — single women without kids — were taking less time to find new jobs compared to similar men. In fact, single women who weren’t moms had a 29% greater chance than single men without kids of finding a new job.
The study didn’t examine the reasons behind the disparities, but [sociology graduate student Brian] Serafini has a pretty good idea what may be at play. “When making hiring decisions, employers have assumptions about mothers,” says Serafini. “There are stereotypes that they will be less productive employees because they will have to pick up their kids and leave work early.”
That is one possibility, but looking at only employer attitudes might be an overly limited perspective. Obviously, the choices made by moms matter as well, regarding how hard to search for work, which jobs to apply for, and so on.
Mothers have a higher standard for jobs they will take, because their work as child-care givers is valuable. Imagine two otherwise identical women, one with a young child and the other childless. Picking some random numbers, suppose they each have a reservation wage (the amount they must be paid to enter the labor market) of $15,000 and further suppose it will cost $5,000 per year to hire someone else to take care of the child while the mother works. If the childless woman is offered any job paying over $15,000 she will accept, but the mother must be paid over $20,000 for work to be worthwhile.
Looking for a job requires effort spent on search, and all else being equal, the higher wage you want the more searching will be required. If mothers are also more picky about the non-pecuniary aspects of their jobs as well - flexible working hours, health care benefits which cover dependent children, etc - it adds another dimension to their search process as well.
Observing different amounts of time searching for a job is not enough to demonstrate employers are discriminating against moms; the choices that different women make due to their life circumstances also have to be controlled for. The conclusions drawn by these sociologists are premature, because they ignore women's agency in the job search process, and assume all differences are due to employers.