If you are thinking of complementary insurance, it is a good idea and you should apply for it before the child is born, as there is no refusal or checks.
Complementary offers a lot more than dental that may be useful for babies, such as some reimbusement for days at home caring for sick children and more freedom in choosing specialists. You can always cancel after the min period (3 years nowadays) or if you leave the country.
As far as dental is concerned, usually you don't pay this element (it is waived) for the first 3 years as babies have no teeth of course. Then note you are likely to use during regular checks and the occasional filling, all covered...
Should it come to braces, if it is simply cosmetic the complementary insurance pays or you pay yourself. But it is really badly needed (teeth growing in all directions etc) then the Invalidity Insurance of the child pays (ie not the health insurance, the AVS/AHV) as it considered 'disability' in the sense that if left untreated it will affect the future life/welfare of the child. The dentist judges that and fills out the necessary forms, it is quite common, so many people get them free or nearly free regardless of insurance.
Thanks to everyone for your responses, I think I've decided to take it before the child is born. If you know some good options other than Helsana, Groupe Mutuel, please throw them in, so I'd check them as well. Otherwise I got responses I wanted =)
Yes - also check Visana - they actually have brace cover as part of "Ambulatory" so you don't need "dental" on top - in case you are interested in that cover.
Agree - most of my kids friends seem to have had them or be having them. Agree also that it may be more cosmetic than strictly needed.
Yes technically but most waive this right as long as you pay the bills. Would be too easy otherwise for this type of insurance to kick you out when you really need it.