Stopping your baby’s potential future "bad" habits before they start sounds almost too good to be true - and it still might be. It’s possible that, no matter what you do, your baby was just born to be a nose-picking, nail-biting, screen-time over-using machine, just like millions of other children, and, eventually, she’ll learn to break those habits. On the other hand, many toddler habits that the adults in their lives despair of are perfectly normal passing phases that don’t ever have to reach the point of being real bad habits.
Many of the traits that adults think of as "bad" habits in toddlers are just things toddlers start doing as a way of coping with the fact that they live in a big, scary world where they’re faced with changes in the environment around them, the expectations people have of them, and even in their own bodies, every day. So this makes them not actually bad, but really rather very normal. Thumb sucking, skin-picking, night-time feeding, nose picking, hair twirling, and pacifier use are all things toddlers use as soothing behavior as they start to assert their independence.
Because these habits are ways for children to self-soothe, shaming or even just calling children out on them can have the opposite effect. Calling too much attention to these actions could cause children to cling to habits they might otherwise have grown out of on their own. Instead, redirecting your baby’s fingers before they make it into her mouth or nose, and then positively reinforcing the redirection can help without making your little one self-conscious. “Isn’t it so nice to use our hands to pet the cat?” can help to keep the habit from becoming too regular while at the same time not drawing too much attention to the habit or reinforcing it with negative attention.
In the end, one of the best ways to keep these habits from becoming life-long ones is by making sure your baby is in a supportive, happy environment where she already gets the attention she needs from you, so she feels less need to lean on habits for comfort. Once she is getting that attention, you can, again, try some gentle redirection or correction from habits that can be harmful, like skin-picking or nail biting, which can lead to infections, or thumb-sucking, which is generally perfectly normal when it begins, but can cause dental problems if it is still going on when adult teeth start coming in at around 4 or 5 years old.
Fortunately, some habits, like whining, nighttime feedings that last well into the toddler years, carrying around a sippy cup, eating for comfort, and excessive screen-time are behaviors you can help stop before they really get started by acting in ways that don’t foster them now. Weaning from night feedings can be a challenge (though your sleep schedule will probably thank you eventually), but it will help out your baby’s teeth in the long run. Setting boundaries you don’t go back on just because your baby isn’t happy with them can help head whining off before she ever falls into the habit of it. And incorporating limits on her screen time early in her life means they’ll feel more natural as she gets older.
Like it or not, your baby is probably going to develop some habits that you don't love, and that's okay. So long as you stay loving and supportive, and your baby's habits don't involve something like throwing dirty diapers at the walls, there's really nothing to worry about.