The major dental organizations in the states like the ADA recommend taking kids in by age 1. However, it used to be age 3. My dentist (who by the way is the most awesome dentist in the whole entire world
) says she sees no reason to start until around age 3. This is in line with what all of my friends with kids have said their dentists recommend as well.
I took my daughter when she was about 3 1/2. She had never been to the office or anything, and she did fantastic. Of course the staff there is super, and we had talked a lot about what was going to happen in the weeks leading up to it. She was actually really excited to go. All they wanted to do was to get her used to the chair and looking in her mouth. They weren't going to make her do anything she did want to. But she let them examine, scrap, floss, and brush. The only thing she didn't like was the polishing thing, so we skipped it. She did that at her next visit though no problem.
It's my understanding that kids should not use fluoride toothpaste until they can reliably spit it out 100% of the time. That's at least what our dentist recommends. I started my daughter when she was around 4, maybe a bit before. Before that, I used Weleda Children's Toothgel for her, and I still use it for my one year old. It's a European (Swiss?) company, so if I can get it here, I seems like it would be available in France.