They can visit Canada and the Caribbean as part of the visa revalidation program. Google it.

It’s correct. 2nd year APs cannot leave the country unless they get a new visa issued abroad.

I have heard this as well, but current au pair decided against going to Canada.

I don't know about Canada, but when my prior au pair was considering extending, our LCC told her that she could get a new visa in her home country (Austria) during a planned trip home over Christmas (which was in the 11 month of her first year) as long as she was already matched with a new host family (she was planning on extending in a different city). She ended up deciding not to extend so she never tried to do so. And, yes, this does mean that she re-entered the country with only 3 weeks left of her visa, which our agency advised against but we allowed her to do and she had no problems.

We are going to extend with our current au pair. She has heard that some APs who extend will either go back to their home country, or to Canada, and get a new visa for the 2nd year. This enables them to travel outside the US during their 2nd year. Is this right? I thought that the visa they get is what they're stuck with even if they stay the full 2 years. Can someone confirm that what my AP heard is true? I hope it is, b/c I know she'd like to be able to visit home during her 2nd year.