The new law comes into effect on Wednesday and will affect all children under the age of 12 - even if they're just passengers on the bike.
Failure to do so can result in a fine of €90 for the parents.
The law change was already published in the Journal Official online bulletin in December, which gives details of laws and official announcements in France.
In other words, parents have had three months to fork out for a new helmet for their kids, so it's probably not even worth trying to talk your way out of a ticket.
In fact, authorities hope that the new law will have a knock-on effect for adults, who very rarely wear helmets while cycling in France.
"If parents aren't wearing helmets, their children will ask them about it. We want to pass on the message through the voices of the children," Emmanuel Barbe, the government's road safety tsar, told Le Parisien newspaper.
And it's no surprise the government is taking cycle safety seriously - France saw a 7-percent hike in cyclist road deaths last year. Some 26 children have died from bike accidents between 2011 and 2015.
And wearing a helmet can reduce the risk of a serious head injury by 70 percent, the risk of minor injury by 31 percent, and the risk of facial injuries by 28 percent, according to France's road safety guide Sécurité Routière.
Several other European countries have helmet laws in place for children, including Malta, Sweden, Slovenia and the Czech republic, according to the European Commission.
It adds that in Spain, cyclists have to wear a helmet outside urban areas except when going uphill.