The alert follows the case of three London schoolgirls - Shamima Begum, Amira Abase, both 15, and Kadiza Sultana, 16 - who fled to the war zone via Turkey during a half-term break in February.
"I have been in regular contact with two head teachers from schools in west and east London who have voiced concerns over their students being "groomed and seduced" by Islamic State (IS) online, Nazir Afzal, former chief prosecutor for the UK's Crown Prosecution Service (CPS) was quoted as saying by The Times.
"One head said he was being approached almost on a daily basis by parents who fear their kids are about to go to Syria.
"Both said they were scared of the Easter break and would be very relieved if all their pupils came back after the holidays," Afzal said.
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"They didn't know what to do. They're told to direct parents to the police, but the parents don't want the police to be told and the heads don't want to criminalise their pupils. They wanted to know why there was no therapeutic, preventative option for these children," he added.
Several schoolchildren have already slipped into militant-held territory, including the three girls from Bethnal Green Academy in east London.
They waited until the school break before paying cash for direct flights from London to Istanbul and are now believed to be in the IS stronghold of Raqqa.
Their parents have admitted that some of this may have been raised by selling family jewellery.
It also emerged last week that five more girls from the same school have had their passports confiscated by anti-terror police amid suspicion that they were also planning to travel to join IS.
"Communication between police, schools and parents was in need of vast improvement," Vaz said.