Nail biting DD, 5, should I try stop it?

[chixinthestix]

DD bites her nails - not very noticeably but realised a few months ago that I hadn't cut them for ages. DD said you don't need to cut my nails Mummy I just bite them off. Despite me telling her not to she's continued. They don't look chewed off, just very short. I never see her biting them so I think she only does it when one gets a bit long, its not a nervous action or anything.

Should I try to do something to stop her or see if she grows out of it?

My 4 year old bites his nails too. Its not very bad, but it's a habit I'd rather he didn't have. A friend has suggested using 'stop and Go'. I've also read that the best thing is to distract them when they start biting, but as he tends to bite his nails in bed when he's going to sleep, I'd rather not use this tactic!