Sydney - The Australian government will be able to strip the children of extremists fighting overseas of Australian citizenship under controversial legislation introduced into parliament on Wednesday.Details of the so-called Allegiance to Australia bill were unveiled as the mother-in-law of one man believed killed in Iraq while fighting for ISIS pleaded for his wife and children to be allowed to return home.Karen Nettleton, the mother of Khaled Sharrouf's wife Tara, said her daughter had made the "mistake of a lifetime"."Today she is a parent alone in a foreign and vicious land looking after a widowed 14-year-old and four other young children," Nettleton said in a statement released by her lawyer.Sharrouf and his best friend Mohamed Elomar shot to infamy last year after they and Sharrouf's 7-year-old son were pictured holding the severed heads of Syrian soldiers.Prime Minister Tony Abbott said the government had a "high degree of confidence" Elomar had been killed but was less sure about the fate of Sharrouf, following reports they both perished in a missile strike last week.Under the proposed legislation, dual nationals like Sharrouf and Elomar would automatically lose their Australian citizenship on the grounds of fighting for a terrorist organisation overseas. A terrorist organization is determined as such by the government as one that is "opposed to Australia, or Australia's values, democratic beliefs, rights and liberties."Civil libertarians have objected to the automatic stripping of nationality based on government definitions of what constitutes terrorism and terrorist activity. The government said decisions would be open to a review by the courts, although this avenue of appeal is not stated explicitly in the bill.The law can also be used retrospectively on people already in jail on terrorism offences. Children of outcast dual nationals can also be banished, although they may claim their Australian nationality via another "responsible" parent.Nettleton said her daughter and grandchildren, one of whom she says was forced into an arranged marriage with Elomar, were desperate to come home.Abbott said the children would be "dealt with in the same way that the family of criminals are normally dealt with." He did not rule out laying charges against minors.The rights of people holding Australian citizenship only are still under consultation.Australia is on high alert for attacks by radicalised Muslims or by home-grown militants returning from fighting in the Middle East, having raised its threat level to "high" and unleashed a series of high-profile raids in major cities.