Haydock's commentary quotes venerable (is he not a saint yet?) Bede as pointing out the similarity in words used in the parable of the lost sheep
In the same way your Father in heaven is not willing that any of these little ones should perish. > Matthew 18:14 NIV
Here, little ones means sheep, which usually means whoever follows the shepherd. The shepherd being Jesus. The key component of sheep-hood is obedience and humility (at least the humility of knowing you're a sheep)
But, more to your question, there's nothing wrong with having lots and lots of explanations of the Bible. I think that Jesus is talking about real children here because He taught with examples all the time ("see that poor woman over there, she gave more than you bums"). So, the literal interpretation is little ones = little people and that should do a little to give any pedophile priest a bit of pause while reading that Gospel.
The metaphorical sense is that little one means freshly minted or potential Christ follower (which would include children) since hindering these folks on their spiritual journey could have gave consequences grave punishement is afforded the purpotrators.
The moral sense of "little ones" might be that little ones are those that it is incumbent on all the teachers of the faith to pass on to their students authentic teaching that will not confuse them or encumber their spiritual growth.
The eternal sense tells us of the punishement due to those who were given much but stink at passing it on. Which is why I approach each year of Catechism Class with fear and trembling.