With the raising of the school-leaving age, more and more children are taking part-time jobs. At the last count there were over half a million children at work. Many children benefit from the experience work brings - and the extra money. But others are exploited by thoughtless employers in jobs which are potentially dangerous - even lethal. As a safeguard every child of school age needs a permit to work. But few parents know about work permits - fewer still care. A jumble of local byelaws - and a shortage of those whose job it is to enforce them - adds to the confusion. JEANNE LA CHARD talks to parents, to the children who have the jobs and to those who try to enforce the law.