THE old adage ''not in front of the children'' has taken on new meaning for an Adelaide woman who has been required to give the Family Court an undertaking not to smoke in front of her two asthmatic children. In an Australian first the judge sought a written guarantee from the woman and she could be dealt with under contempt of court laws if she breaks it. The case, not unusual in the US, is expected to be followed by many similar orders. Already a Melbourne man has applied to stop his former wife smoking in front of their children. And it comes as a national inquiry begins into whether pregnant woman should be legally prevented from behaving in ways harmful to their unborn child - smoking, for instance. The mother, in her 40s, who has custody of her two children who are both younger than 10, was taken to court by her former husband who sought injunctions to stop her smoking in front of them and subjecting them to passive smoking. The lawyer for the children's father, who has remarried but has fortnightly access, told the court their mother's smoking was affecting their health and they smelled of smoke after being with her. Justice Thomas McGovern refused to issue an injunction against the woman, who cannot be named under Australian family law, and accepted her word that she smokes outside now. Her lawyer, who said the children's asthma was hereditary, affected by seasonal conditions and viral infections, told the court she smoked about three-quarters of a packet of cigarettes a week, but had already recognised the dangers of smoking in front of the children. Reaction to the case has been mixed with the Anti-Cancer Society applauding it but hoping other such cases would not be needed. But the South Australian Law Society's president, Rod Lindquist, said the ruling was an extraordinary approach. ''Does this case mean the court can rule that a custodial parent cooking lamb chops would be required, for reason of health, to cut off the fat?'' he said. In fact, that may not be far-fetched. The Australian National University's law faculty has begun an inquiry into foetal welfare and the law which aims to determine whose responsibility it is to provide the best care for a foetus. It will not only look at whether the law should stop pregnant mothers behaving in ways harmful to their babies - smoking, drinking alcohol, taking legal or illegal drugs, exposing it to passive smoking, for instance. It will also consider whether the baby should be able to sue its mother if it is damaged by her behaviour or sue a third party such as a cigarette company. Inquiry member Dr Ross Sweet, senior vice-president of the Royal Australian College of Obstetricians and Gynaecologists which is funding the inquiry, says a foetus has no rights under common law but, when it is born, gets some retrospective rights. The inquiry will look at doctors' responsibility to warn pregnant women of behaviour that could harm a foetus and at the legal position if a doctor failed to give such warnings. Legislative and judicial involvement in pregnancy is not unusual in the US and some aspects of that involvement have been highly controversial, with feminists saying that the mother's rights have diminished as the foetus' have increased. In the late 80s ''foetal neglect'' legislation was introduced to a number of US state legislatures, with the behaviour deemed negligent ranging from not following doctor's orders to eating the wrong food to giving birth at home. In Australia such cases have not yet reached the law books, although there are concerns that the Adelaide smoking case may mark the start of a trend in that direction.