Thumb-Sucking Teeth

It's so sweet to watch a newborn suck their thumb as they sleep, but is it bad for them to suck on their thumbs? Can it affect their adult teeth? After some research I found that it can cause a condition called thumb-sucking teeth which can be a really big deal. I also found that while it should be perfectly safe for the first couple of years, it really should be stopped by the time they are a toddler.