I agree with Mrs Geek. I assumed that nail biting would be a 'learned habit' which in the majority of cases it is, little girls at school see their peers biting their nails and join in, the mums that I chat to can vouch for this. However, my son who is now 3 1/2 started biting his nails when myself and my husband were going through severe marital difficulties when he was about 2 1/2. None of my family bite their nails so I don't believe it could be a learned habit. Incidentally, the nail biting also coincided with the loss in a local supermarket of his comfort toy 'kitten'.
My belief is that the stress of what was going on in the family and the loss of 'kitten' stressed him in to biting his nails.
I am happy to say that now everything is back on an even keel he is less of a biter and grows his little and ring finger on each hand and I feel sure that although he now has a habit, that everything is happy at home, he will lose that habit.
There has to be a reason why very young children bite their nails and the root cause should be sought before we start painting their nails at such a young age with foul tasting substances!!!
Kids have to see and feel so much more than we did at their age...the 21st century?.....