My 2-1/2-year-old son has just recently begun biting his fingernails. For the last three or four weeks I have been repeatedly been removing his fingers from his mouth when I see him biting his nails and trying to distract his attention. I have asked his caregivers at daycare to do the same. Basically, he just proceeds to put his fingers back in his mouth immediately or very shortly after I remove them. He is extremely strong-willed and determined. Do you have any suggestions as to how we can curtail this activity before it becomes a strong habit?
If you have a strong-willed 2 1/2-year-old (a rather redundant phrase), he will "win" this power struggle because you cannot be around him all the time, keeping him from biting his nails. At this age and stage he is aware that he can say NO to you in a variety of ways and become more autonomous. He is getting something positive from this habit. Although it may be difficult to pinpoint, pay close attention to what precedes his putting his fingers in his mouth. There may be clues that suggest a pattern. Sometimes it's nervousness, tiredness, boredom, hunger, etc. Ask his caregivers to pay attention also. If there is a pattern, then you may be able to interrupt his finger biting response before it manifests itself and begin introducing another response and/or activity.
If you keep his nails as closely trimmed as possible so there's really not much to go after with his teeth, that may discourage him. Some parents have made up a "recipe" of a sour and or peppery liquid and dipped their child's fingers in it; many have reported that this simple behavioral conditioning technique works well. They have made it liquid enough so that it is like dipping fingers in water, yet potent enough so that the tongue responds immediately to the taste sensation. Obviously one needs to test it out so as not to shock the child's system.
I think calmly taking his fingers out of his mouth and then taking that hand and leading him somewhere else is OK. I would be cautious not to follow the finger removal with a fun activity since he might become conditioned to think that biting his fingers will lead to a special time with you.