The personal habits of some children may disgust or annoy adults, but carers can see them as a guide to a child's emotional state, says Juliet Brown Common childhood habits - rocking, thumb-sucking, hair-twiddling, nose-picking and nail-biting - are repetitive ways of providing comfort and reducing tension. Most children try out one or other of these forms of self-comfort and stress reduction before they reach school age. Whether the habit persists can depend...