I took my 2 year old to the dentist a few weeks ago and she said I should have been flossing already. If nothing else, to help encourage the habit. She said those little flossers are great, the ones shaped like animals and such by the kids' dental hygiene products. My son still does not have all of his teeth. But, the earlier the habit is instilled, the more likely he is to pick up on healthy dental habits for a lifetime. (Which is why I started taking all my kids to the dentist young.) My older 2 started flossing around 3 years old??? The oldest is still in her good habits, but the 2nd one I'm always having to make sure she's done what she's supposed to do. She is 6.
To all here: as someone who has lost several family members to heart disease, remember that poor dental health leading to poor gum health is a leading factor in heart disease. Flossing is VERY important. How else would the in-between's of your teeth get cleaned without it. (Nasty if you think about it. Never flossing = they are never clean.) Also remember to floss behind your back molars, as most tooth brushes cannot get that part clean. Also, flossing helps clean your gums in between also. There is absolutely no reason to not teach your child to do it as early as you can!
You're doing a great job with your 9 month old! Those little flossers are fun, pick up a pack and start with those. :)
The comment below about her losing her baby teeth so no reason to get hung up on it is a very common misconception also. Did you know that if baby teeth have cavities / rot, it can be passed on to the permanent teeth? On my son's X-rays he took at just 2 years old, his permanent teeth were already formed and sitting above and below his baby teeth just waiting for the right time to come in. Very important to take care of those baby teeth so that they don't pass any cavities or rot onto those permanent teeth before they even have a chance! You only get one set of permanent teeth, and children are still very young when those start coming in!