Once our LO is starting to talk and gabber away we have a tutor who will come in and teach him French, he'll continue it through nursery and the school he's going to also do French tuition twice per week after classes. I'd say roughly around the 18 month marker is when we'll start with him, obviously it depends on his individiual needs and personality etc it might be 12 months, might be 20 months....we'll see how we go.
I speak English & Welsh (thanks to Welsh Grandparents who refused to speak in English untill just a few years ago!) but I see it as somewhat pointless in teaching him to be fluent in a language that won't ever help him much - I'm sure he'll know the odd sentance, phrase, word etc to help with politeness etc but I'd rather stick with the French. Welsh can come third if he really has a flair for languages.