The teaching on "limbo" was nothing more than an unfortunate attempt by some catechists to explain something that was, and still is, a mystery. To this day we don't know where the souls of the unbaptized, who had not committed an "actual" sin are consigned. The Church, knowing that such a soul could go neither to Heaven, nor Hell, clumsily crafted the teaching on limbo, rather than just admitting that it's a mystery.