I hate to say it, but there is alot of fear telling out there about thumb sucking / pacifer sucking causing problems... What I hate is everyone saying "don't let your child do that because...." when there is absolutely <B>NO</B> proof that those things cause an under or over bite.
My eldest child sucked her thumb until she was 5 years old. No problems there at all. My middle child didn't have the need to suck, yet he has problems with his teeth. My youngest child used a pacifer (24/7 it seemed) until just before her 3rd birthday. She has no problems at all.
Some children <B>need </B> to suck. It's as simple as that. To deprive you child of something that he/she needs is not our job as a parent. Some children don't have that need, but for those that do, I honestly believe that there is no harm to be done in allowing the child to suck the thumb or pacifer up until the child decides it doesn't need it anymore.
<I> just my opinion </I>
peace