Crowds of well-wishers have gathered in the French Alps town of Annecy to show solidarity with victims of a playground stabbing attack that left four young children and two adults injured.

Annecy mayor Francois Astorg called for a “citizens’ gathering” in the lakeside park where a man with a knife launched the attack on Thursday.

People have piled flowers, toys and messages of support on the playground’s padded surface in the days since the attack. A pink heart-shaped balloon tied to a bench had the message: “For the children – love.”

The children targeted were a 22-month-old Dutch girl, a three-year-old British girl, and two French cousins, a boy and a girl, aged two. They received serious injuries and remain in hospital, though their conditions have improved to the point where their lives are no longer in danger, the regional prosecutor said on Saturday.

One of the adults injured, a Portuguese man who was knifed while trying to stop the attacker from fleeing and was then shot by police as they detained the suspect – also remains in hospital.

Multiple bystanders sought to deter the assailant, including a French Catholic pilgrim named Henri who repeatedly swung at the attacker with his bag and has been dubbed “the hero with the backpack”.

The suspect, a 31-year-old Syrian refugee with permanent Swedish residency, was handed preliminary charges on Saturday of attempted murder and armed resistance.

Witnesses told investigators that the suspect mentioned his own three-year-old daughter, his wife and Jesus Christ during the attack, regional prosecutor Line Bonnet-Mathis said.

Preliminary charges under French law mean magistrates have strong reason to suspect wrongdoing but are allowing more time for investigation before deciding whether to send a suspect to trial.

The stabbing suspect refused to talk to investigators, and was examined by a psychiatrist and other doctors who deemed him fit to face charges, the prosecutor said. She said the motive remains unclear, but it does not appear to be terrorism-related.

The suspect remains in custody pending further investigation.

Local authorities are providing psychological support to the victims and their families, as well as to traumatised witnesses.

Among those in the park at the time was a group of high school students on an end-of-year field trip, some of whom reportedly protected younger children from the attacker.