Parents and caretakers pushing around — and valet parking — high-priced baby strollers. The average rent for just a one-bedroom apartment is $2,644, up from $1,503 in 2009. These are some of the reasons Brooklyn’s Park Slope neighborhood has earned a reputation for affluence. But that’s not stopping the Fifth Avenue Committee (FAC) from fighting to preserve and even grow Park Slope’s supply of affordable housing.