Both candidates have publicly spoken to supporters after the vote about their plans.
Ahead of the vote, surveys suggested Le Pen was faring much better among voters under-25 than among the population at large, often by a margin as high as 7 percentage points.
"They can be in agreement with us", said Steeve Briois, the mayor of Le Pen's northern bastion of Henin-Beaumont, adding that those far-left voters sought choices "outside the system".
French far-right president candidate Marine le Pen is accusing rival Emmanuel Macron of being "weak" in the fight against Islamic terrorism.
One vendor, who did not wish to be named, accused the two candidates of trying "to be seen in the same light as people who really are hard-working".
Marine Le Pen has resigned as leader of the Front National, saying she needs to be "above partisan considerations" in her battle for the French presidency.
Mr Macron - who ran under the independent En Marche!
France's divided political mainstream, rejected by an angry electorate, united Monday to urge voters to back Macron and reject Le Pen's far-right agenda. (On The Move) banner - won 23.75% of votes in the first round, while Ms Le Pen won 21.53%. The Nasdaq Composite hit a record high yesterday, while the Dow and S&P 500 brushed against recent peaks as strong earnings underscored the health of corporate America.
The BBC's Hugh Schofield in Paris says this is a symbolic act meant to show her concerns are for the country as a whole and not for her party, and that she is reaching out for the voters of candidates defeated in the first round, particularly those of the Republicans' François Fillon.
She added: "He is a hysterical, radical "Europeanist".
France's centre-right party, seeking to rebound after the defeat of its presidential candidate, said on Wednesday it could share power with Emmanuel Macron if he is elected, as pollsters predict, on May 7. Since then, she has been working to softening the party's image by targeting widespread support of young public and workers.
Le Pen's father, Jean-Marie, made it into a presidential runoff against Jacques Chirac in 2002 and was crushed.
Wearing a white jacket with the market's logo, the blonde 48-year-old National Front (FN) politician meandered through the aisles, a retinue of party officials in tow. Turnout was 78 per cent, down slightly from 79 per cent in the first round of presidential voting in 2012.
Dominique Reynie, head of the Foundation for Political Innovation think-tank in Paris, believes Le Pen will not be elected because most French people worry about her scrapping the euro.
Protesters overnight burned cars, danced around bonfires and dodged riot police at the Place de la Bastille and Republique.