This is is a great study: young babies—those too young to talk—exposed to bilingual environments develop a variety of mental skills not seen in babies from monolingual homes.
It's a great study, but the journalism points to a sickness in our culture. More below. First, what are we talking about?
The researchers taught bilingual and monolingual babies to look at one side of a screen in anticipation of a visual "reward" image of a puppet, after the infants first learned to associate a sound cue with the image. The visual treat was then switched to the other side of the screen, so that researchers could see how quickly babies would learn to switch their anticipatory look to that other side.
Bilingual babies beat out monolingual babies in three such experiments, even when the sound cues changed from nonsense syllable combinations to a structured sound cue, and then a visual cue. In all three cases, bilingual babies soon learned to switch their anticipatory attention to the other side of the screen, whereas monolingual babies never adapted.
As a fan of languages, I think this is a hoot.

But I don’t think any great moral lessons are to be drawn here; and as a parent of a 9-month old myself, I am a little wary of competitive parenting. Even the smartest kids grow at different rates. My two and a half year old, for instance, is a little behind the curve in speech, and a little ahead in reading. It’s not a big deal.
But some parents at the playground get highly defensive and even antagonistic when another kid beats their own at anything. There’s a hyperdrive in our parenting culture these days, so I see stories like this and know how it will be turned around into more competitive parenting. Alas.
The researchers insist that the babies' acquired skill has no bearing on IQ:
... enhanced executive function does not necessarily translate into better intelligence — and in any case, monolingual babies have plenty of opportunities later to exercise executive function.
"My conclusion is that it's a very particular component of our cognitive toolbox, and early learning certainly has no negative effect," [lead scientist] Melher said. But despite suggestions from other researchers, he personally doubted whether such early bilingual training leads to improved IQ or better test scores.
Even so, the fierce culture of competitive parenting will guarantee tons of page views (and therefore advertisement views) for a an article promising tools for getting your baby into Harvard. Look at the hyperlink above to the story: the url ends with: bilingualbabiesgetanearlyedge.
"An early edge"? Nevertheless, I will continue to sing my dumb Swiss hiking songs while spooning rice cereal to the beast. Because it’s partly for my own sanity.