Molly, I don't know if they are the same over there, but these are sort of large bags full of nutrient packed soil that you lay flat and open at the top, allowing you to plant stuff directly into them.
like these..
handy 'how to' guide..
BBC - Gardening - Basics - How to use a growing bag
You can get kiddie type ones too, that you can get your kids to plant little things like flowers and herbs in to give them a taste for it..
