GendarmerieFour people, including the grandparents of Emile Soleil, have been arrested over the two-year-old's disappearance and death in the French Alps in July 2023.
The two other people arrested on suspicion of voluntary homicide and concealment of a corpse are adult children of Emile's grandparents, prosecutors said in a statement.
The grandparents' lawyer, Isabelle Colombani, told AFP on Tuesday morning that she had no comment, having "only just heard" about the development.
Last year, some of the toddler's bones and clothes were found by a hiker near the home of Emile's maternal grandparents in the French Alps, where the boy had gone missing the previous summer.
But prosecutors at the time said that the remains offered no further clues as to the cause of Emile's death, adding that it could have been as a result of "a fall, manslaughter or murder".
Tuesday's sudden twist, in a case that seemed to have gone cold, made headlines in France, where the search for Emile has been extensively covered by the media. When the toddler disappeared, dozens of journalists flocked to Haut-Vernet, often outnumbering the 25 residents of the tiny Alpine hamlet.
The last sighting of Emile had been on 8 July 2023, when two neighbours saw him walking by himself on the only street in the village.
Police were alerted by his grandmother shortly afterwards. Hundreds of people joined police, sniffer dogs and the military in a search the following day.
Initially, French reports focused on Emile's grandfather - but his lawyer said that she hoped investigators would not "waste too much time on him to the detriment of other lines of inquiry".
Emile's remains were found days after police summoned 17 people - including members of Emile's family, neighbours and witnesses - to reconstruct the final moments before the boy disappeared.
The toddler's funeral took place in February this year. Soon after, his maternal grandparents said that "silence had made space for truth" and that they could no longer "live without answers".
"We have had 19 months without a single certainty. We need to understand, we need to know," they said.
In a statement, Aix-en-Provence chief prosecutor Jean-Luc Blachon said that Tuesday's arrests were the result of investigations carried out over recent months, and that police were examining "several spots in the area".
French media reported on Tuesday that the grandparents' home in the Provence region was being searched and that police had seized one of their vehicles.
In France, people can be placed under arrest for questioning while police investigate whether they may have been involved in a crime. It does not mean legal proceedings will necessarily be started against them.
