The admission came as the Government said it is to consider a national registration system for childminders following the case of Helen Stacey, who was jailed for life this week for murdering a five-month-old Norfolk boy.
Stacey had not disclosed her previous married name, so checks failed to pick up her convictions for prostitution and the fact that two of her own children were adopted and a third taken into care.
Ronnie O'Connor, Glasgow's senior depute director of education, said: "What we don't know about are cases where parents don't ask for a registered childminder, where nannies are hired or where there are private childminder services operating, in which case we would have to rely on members of the public whistle-blowing."
The education departments in the 12 authorities which succeeded Strathclyde are responsible for registering childminders, and other provision for children under eight, in line with the 1989 Children Act. The former region had integrated education and social work pre-fives services with education in the lead. This approach was also followed in Central Region and adopted by Stirling and Clackmannan councils.
Mr O'Connor says Stacey's failure to give her previous married name and reveal that her own children were in adoption and care would have been picked up, because Glasgow requires inter-agency referrals and checks are made through the Scottish Criminal Records Office.
The SCRO check would have demanded all names and previous addresses. References would also have been sought from a family doctor and these would cover everyone else in the applicant's household. If potential childminders have children under the age of five, a report is requested from the health visitor. Finally, applicants have to give a reference from two people who have known them for at least two years.
Registration lasts for a year only and is then reviewed. Glasgow has 352 registered childminders and the council has a staff of 16 dedicated to vetting childminders and nurseries.
But Sandy Wilson, education officer responsible for under-fives in Clackmannan, said: "If someone deliberately sets out to cheat the system, nothing can be a hundred per cent foolproof."
The Scottish Criminal Records Office, which handles up to 120,000 checks a year, says any application with an English address is referred to the relevant police forces south of the border or to the police national computer.
Pressures on the SCRO are set to grow substantially, however, as all adults will shortly have to be cleared to work with young children in voluntary organisations, following the Cullen report into the Dunblane shootings. At present the office deals only with health board and local authority staff.
Childminding has mushroomed over the past decade, from 2,389 registered minders looking after 5,159 children in 1983 to 8,593 minders responsible for 35,981 child places in 1996.