What is important is that you get involved. This is what will really get your kid's attention. Listen to a French CD and sing up a couple of words, enticing your toddler to do it as well. Sit down with your child while you watch a Disney movie in French and use simple sentences like "regarde! Mowgli mange une banane!" Get up and dance, and repeat “une banane! Une banane!” sing along with the songs, your children will love this special time and will definitely develop an ear for the language -- and associate it with a special bonding time with you.
You would like your children to speak French one day so why not start when they are toddlers? Although many parents' first reaction is to hire the help of a tutor, a one hour a week exposure to a tutor is not going to do much for a toddler or a young kid. Kids learn by repetition -- constant repetition -- and learning a language is no different.
The best solution would be to hire a French nanny to speak with them all day, or move to France -- but this is not an option for most of us. And what about the ever so sought after French playgroup? I never found one myself, so good luck with that...
If you want to successfully teach French to your children, you have to make up a plan of action, and stick to it in the long run.
Be firm and consistent
Don’t forget though, repetition is the key. And it’s likely that at one point your kid is going to show some resistance. Like wanting to watch TV in English. If you give in ONCE, then it’s going to be a struggle each and every time. Of course your child will prefer doing what is easier, and hear English. But we all know the attraction TV has on kids. So use it, present TV as a special treat. And that treat comes only in French, so it’s French TV, or no TV. Same goes for music, stories etc... See the tools I personally recommend here.