I think a lot of backgound noise (talking) is not supposed to be good, but I from hat I gathered (and did), when DS was a baby, I'd put it on for a few hours, though much of which he napped, and I'd rotate with music. It was some talk, but I was home alone with him in an isolated rural area with patchy internet and I needed the ideas and the "company".
As for the "not realising how much they absorb", my DS is almost 4 and we are listening and the radio says "This is Michele Norris..." and DS chimes in "IN WASHINGTON! Mama, where's Washington?"
. We don't listen to any of the involved or violent stories, just the basic news and some other pre-school friendly shows occasionally. And here, we're kind of limited anyway, as the news and talk programs end at 9am and don't start back up until 3:30 or 4 and in-between is "diverse music" and at 7pm starts some of the other programs (like "Fresh Air"), so that's cool. It's kind of varied anyway. But we certainly don't listen all day.
Enjoy it while you can. My son was introduced to the Wiggles CD's by my in-laws and now I have to bargain for NPR time against "the big red car"