Abdalmasih Hanoun, a Syrian refugee, apparently spent hours sat on benches less than 50 feet from the scene of Thursday’s attack in Annecy.
French Prime Minister Elisabeth Borne confirmed that the victims - aged between 22 months and three years - all underwent surgery and are now in a stable condition.
On Friday, Hanoun's custody period was extended amid reports he was refusing to leave his cell and "rolling around on the floor".
One boat hire vendor near the playground in Annecy said: “He was here pretty much everyday unless it was raining.
“He would normally wear the same outfit - black trousers, white shirt and something on his head - just like in the video.
“He would just sit on the bench and do nothing.”
Another said: “We seen him here for at least a month. He seemed calm, nothing special about him.”
Hanoun lived a normal life in Sweden where he was before coming to France, according to reports.
Swedish daily newspaper Aftonbladet said he had lived an “ordinary life” and studied English and Swedish as second languages.
It is reported that he claimed three times for Swedish citizenship with no success.
The comments from locals came as tearful well-wishers visited the playground to leave flowers and messages.
A British mother of two, Katie Jackson, 39, was in tears as she said her son had asked to visit the park on the day of the attack.
Ms Jackson moved to the town three years ago with her husband. She has two sons, Rudy, five, and Vinnie, nine months.
She said: "Locally we call this the pirate playground, because it has a pirate ship in it, it's a place that our kids know and love.
"It was my son's fifth birthday yesterday and he had mentioned he would be interested in going to the pirate place, but he was at school.
"It's a local treasure, that's why it's so shocking. I don't know anyone who hasn't visited the pirate playground."
The Swedish Migration Agency has confirmed the suspect was granted permanent residency in 2013 and although the agency did not identify him, it said he subsequently sought Swedish citizenship in 2017 and 2018, both denied, and applied again in August last year.
Mr Darmanin said the suspect entered France legally, adding: "For some reasons we don't really understand, he applied for asylum in Switzerland, in Italy and in France, which he didn't need to do as he already had asylum in Sweden for the past 10 years."
Local prosecutor Line Bonnet-Mathis said one of the adults was seriously injured by both a knife wound from the attacker and a bullet wound from police as officers shot at the knifeman while trying to detain him.
Witnesses said the knifeman shouted "in the name of Jesus Christ" as he launched the attack, including stabbing a child in a pushchair repeatedly as bystanders screamed for help.
Ms Bonnet-Mathis told a press conference on Thursday afternoon the attacker's motives were unclear, but they did not appear to be related to terrorism.
Footage of the attack shared on the internet shows a man in dark glasses and with a blue scarf covering his head brandishing a blade as people screamed for help.
PM Ms Borne said the suspect had no criminal or psychiatric record and appeared to have acted alone.
"We are talking here about infants, very young infants who have been very seriously injured," she told a press conference, according to a translation.
"We are absolutely shaken by all this and we are standing firm by the people of Annecy."