Eberhard van der Laan said more than 50 parents had been informed that the suspect arrested last week after a tip from U.S. authorities has either confessed to abusing their children, or was thought to have done so.
"This is about a serious suspicion of grave abuse by a man who was arrested Tuesday and has been held since then," Van der Laan said at a news conference with the city's police commissioner and chief prosecutor.
"I see it as my most important job to inform parents as well as I possibly can," he added.
The suspect was arrested Dec. 7 after a Dutch police television program aired what it said was an image of an unidentified victim of child pornography. The program said U.S. authorities had seized the image in a separate investigation, chief prosecutor Herman Bolhaar said.
U.S. law enforcement officials had informed Dutch authorities they believed the image had been manufactured in the Netherlands.
The victim's parents identified their child from the image and called police, leading to the suspect's arrest the same night, Bolhaar said.
The man's computers containing child pornography were seized and he has since confessed to dozens of sex crimes allegedly committed over the past year and a half, Bolhaar said.
The victims were boys and girls under four years old, he said.
Amsterdam police spokesman Rob van der Veen said Monday police were still seeking more witnesses and information in the ongoing investigation, with more arrests possible.
Mayor Van der Laan urged media not to publish photographs of children possibly affected, and to be reserved in contacting parents.
Police identified the man as a Dutch citizen originally from Riga, Latvia, and also published his photo -- an unusual step, as privacy laws usually prevent publication of photographs of suspects in the Netherlands.
Van der Laan said that the photo had been released in part to reassure the thousands of parents in Amsterdam whose children were not affected.
"At the same time we want to alert others that it indeed was their baby sitter," he said.
Prosecutors said in a statement Sunday they have also arrested the man's 37-year-old partner on suspicion of possession of child pornography. The older man is not suspected of physically molesting children, the statement said.
Bolhaar noted the 27-year-old main suspect was a specialist in encryption and his computers had sophisticated protection.
A 39-year-old employee of one of the day care centers where the man worked was also arrested Sunday after allegedly attempting an "indecent" online chat, the prosecution statement said.
A candle was left Sunday night on the steps of one of the affected day care centers. An attached note bore the single word: "terrible."