When I started playing in the early 70's, we played the 5-3-2 system you described. By the time I was in junior high, it switched to a 4-3-3. Curently, the team of kids I coach (3-4th graders) use 9 players, and I use a 3-2-3 system. I would use a 2-3-3 or a 2-4-2, but I lacked the talent to make either of these systems work. The shift seems to be for (1) more of a balanced presence on the field and (2) recognizing that most of the action takes place at midfield.
As for the keeper, there was fear he was hurt, but he (like all keepers) is a little crazy, so he's playing. No broken bones, just bruises.