Our middle child, a boy, just turned 5 in December, and has always been a finger sucker. I told them that when he turned 5 he would need to stop b/c he will be starting K later in the year and none of his friends at school will be sucking their fingers. He started a two day a week pre-K this year, and never, and I mean never, sucked his fingers while he was there. It has been gradual since the start of Pre-k , but he began to suck them less and less, and finally was only at night, in the car, or when watching TV. Well, I am happy to report that the gradual decline has continued, he had his 5th b-day with the above mentioned reminder, and now three months later falls asleep at night without sucking his fingers! If he gets disturbed while sleeping he sometimes will begin to suck them, but does not use them to fall asleep any longer.
He did all this on his own, no intervention from us. I just gave him time. This is a very current situation that has just resolved for us, and I will be glad to give you further info or encouragment if you want, just message me!