Not much advice here - as it took a very long time for me to enforce. My middle child (I have 3 children, 7, 9, and 10) sucked his thumb into first grade. I'd tried everything I knew of (1) the nasty polish ... he'd suck it off, (2) the socks...he'd pull them off after a bit, (3) asked Dentist about T4K trainer...Sonshine Dentistry in Noblesville...but he was missing teeth at the time, and they preferred to wait until the space was filled before using it...
Nevertheless, eventually he just plain outgrew it. He didn't do it all of the time, mostly when he was without something to do with his hands. So, for us, staying busy helped the most! I had to take the effort to make up little chores for him all of the time to make it stop. It worked by 7yrs old. Unfortunately, death of Grandpa brought back the sucking temporarily. I got back to keeping him busy ... it's stopped. Only thing was Grandma encouraged that it was "OK" to suck to go to sleep.
My poor guy had lost teeth #7 & 10 ... top teeth next to those that are front and center. Well, those teeth have now been out for 1 1/2 yrs...and after being advised by our regular dentist as well...we'd waited for 1 yr, then saw ortho ... placed on a waiting list to get in... now yesterday we had an exam & xrays (previous xrays showed the teeth up high...waiting to have room to erupt) ... well, the damage has been done. The new teeth are preparing to erupt BEHIND his front teeth. He was SHOCKED that his habit had that effect. I think he could encourage other kids not to suck....because at this age, he really cares what he looks like. Orthodontist said it's really not that uncommon, we're going to work on waiting for them to completely cut through, then work to space his palette (he'd pressed it upward, rather than it naturally spreading outward) ... so it'll be a 6-8 month treatment period, the orthodontist expects.
Don't lose heart...I just want you to know that it really can affect their teeth. Oh yes, and my 9 yr old told me yesterday that the real reason he stopped sucking his thumb was because the sucking hard started to cause pressure in his jaw area!
Blessings!