French far-right leader Marine Le Pen proposed Thursday that the children of illegal immigrants should be refused public school places as part of tough proposals to restrict state services.
Ms Le Pen said she wanted to block education for immigrants who are in the country illegally, whereas at present any child of school-going age can attend classes.
It regularly criticises the use of France's chronically over-budget social security system for foreigners, arguing that French people should be prioritised. Fillon is a social conservative who leans to the far right, and was seen to have been picked as a realistic contender to Le Pen.
Latest opinion polls suggest she is running neck-and-neck in polling for the first round with the centre-right candidate Francois Fillon who has projected himself as a radical economic liberal.
Marine Le Pen, who took over leadership of the FN from her father, Jean-Marie Le Pen, has successfully transformed her party into the one of the strongest political forces in France. Although Fillon is expected to win, Le Pen said on the BBC's Andrew Marr Show that Donald Trump's victory in the USA presidential elections in November had "made possible what had previously been presented as impossible".
However, around two-thirds of voters would choose Mr Fillon over Ms Le Pen in the deciding round.
He has also rejected the idea of "multiculturalism", called Islam a problem for France, and insisted the country must defend its traditions, language and identity.
As for immigrants with legal status, "I think there is a certain amount of time for taxes from them before getting access to all the public services, like education, social security", she said after a stop at a stand selling Champagne.
"I would like remind you that it's a matter of honor for the French republic to guarantee to children, to all children, the right to an education - in other words, the right to a future", she wrote.
In response, French Education Secretary Najat Belkacem wrote an entry on her blog condemning Le Pen for her "total indifference to the awful human circumstances faced by young children".
A move to prevent children from accessing education would now be in breach of French law, which guarantees schooling for all children in the country. She has been riding the populist, nationalist, anti-establishment wave that has swept the West.