Thumb sucking is the worst. Even when they are convinced to actively try to stop it still happens in their sleep and the nail polish is useless in my experience. Just leads to a kid spitting in the corner. Ultimately leads to a thumb sucking prevention device and expanders costing thousands of dollars to correct over the course of a year or two. My second son had a pacifier because I was able to assist meaningfully in weaning him off of that. I was not permitted to chop off my first sons pacifier.
My first born wouldn’t accept a pacifier over his thumb and we didn’t know well enough to press the issue. With insurance it cost $3500 that included getting him fitted with a device to stop the thumb sucking, once that behavior was kicked he was fitted with an expander, top one required manual adjustment every week or two depending on ortho assessment. We would go in every month or two to monitor progress along with the occasional trip because an expander broke. He is currently without expander and things have been great for a couple months but in June we go in to determine phase 2 way ahead after things have time to settle, braces likely.
My youngest is five years younger, he was the pacifier user, scheduling his initial evaluation is on my to do list before we go back in June so I can’t speak to a medical difference yet.
I could tell my oldest son had a narrowed elongated jaw structure without formal training though. I was glad we could get everything sorted from that perspective before his adult teeth started impacting anything. I still believe braces will be required to shift teeth around better now that theirs more room.