Not insensitive at all. Fostering is just the first step, and can be followed by a formal adoption. Our three adoptions were foster for ~2 years as the case made its way through the courts (we got all the kids at <1mo old).

Depending on the situation, kids can go back with their biological parents. The social worker should be pretty up front about the prospects of that, though. Of the 5 kids we've fostered, 2 went back to their parents and we were well aware of that before we took them (they were 3 and 6 years old). Usually when infants are removed from a home, there's not much chance of them returning.