Should we swear in front of our kids?

The other day, my toddler son came home from childcare saying "piss poo". He is one of the younger children in his classroom and clearly he heard this phrase from an older child he admired. I couldn't help laughing at this unexpected outburst, which reinforced this behaviour - thus cementing the phrase in his emerging vocabulary. Now he goes around muttering "piss poo piss poo pissy poo" under his breath as he goes about his business. Is this a bad thing? Should I scold him for using words he doesn't know the meaning of? Should I discourage him from using swear words and refrain from swearing in front of him?