Booked on Liberty of the Seas and starting to worry a kid will slip through the railing?
You have nothing to be worried about! There is no way that a child could just slip and fall through any of the railings and right off the edge of the ship. If this were a safety issue you would hear about it happening all the time. Keep in mind that in the stories you hear on the new about someone "falling" off the ship, it is not something that just happens. There are usually many other circumstances that lead to that person going overboard and often alcohol is greatly impairing that persons actions.
Also if you are worried about your balcony railing in your stateroom, that balcony wall is made of plexiglass, so there is no space at all for anyone to slip through. It may help with your piece of mind to spend some time watching some YouTube videos of the ship to get a better view of what all the railings look like. I will say we have been cruising with our kids since my oldest was 9 months (she is now 7) and we have never had any issues or scares!