AUSTRALIA'S first law protecting allergy-prone children at schools, kindergartens and childcare centres came into force across Victoria yesterday.

But peanut butter sandwiches and other high-risk allergens have been off most school canteen menus for years, experts say.

Under new Victorian laws, introduced on the first day of third term, schools and other children's organisations must have a policy enforcing safety standards to deal with life-threatening allergies such as anaphylaxis.

These include training staff to minimise the risk of anaphylactic shock, recognise allergic reaction symptoms and administer adrenaline.

Peanut allergy affects about one in 100 children and about 4000 Victorian children have been diagnosed at risk of anaphylaxis. The prevalence of dangerous food allergies has more than doubled in the past 30 years and Victorian hospital admission rates have tripled in the past five years.

Nigel and Martha Baptist, whose son Alex, 4, collapsed and died at kindergarten in 2004 after a suspected allergic reaction to peanuts, welcomed the landmark legislation as Alex's legacy, referring to it as "Alex's Law".

But the Melbourne couple was disappointed the law stopped short of banning nut products in all primary schools and services for young children.

"Preschoolers and primary school kids often don't understand or have that appreciation of the dangers involved," Mrs Baptist said.

State Children's Minister Maxine Morand said bans were impractical because they often led to complacency and were hard to enforce for all allergens such as milk, wheat, fruit and eggs.

But Victorian Principals Association president Fred Ackerman said an exponential growth in dangerous childhood allergies in the past 8-10 years meant virtual bans were common.

"Allergies are now so prevalent that there would hardly be a school in Victoria without an affected student," he said.

"High-risk foods such as nut products have been off canteen menus for a long time," he said.

Ashburton Primary School, where 13 of the 450 pupils are anaphylactic, has not banned nut products, but has asked parents to keep them out of kids' lunchboxes.

"Most parents have been supportive and teachers can't be policemen searching through lunchboxes every day," principal Phil Webb said yesterday.