A 27-year-old man who worked in at least two nursery schools has been arrested in Amsterdam on suspicion of abusing 30 to 50 young children.
Robert M - as he was named by police - was detained last Tuesday and more than 50 parents were contacted on Sunday.
A spokeswoman for the Dutch public prosecution service described the case as "huge" and "unprecedented".
The suspect was identified after a two-year-old boy's picture was shown on Dutch TV as part of a US inquiry.
Police said he had also worked as a childminder in the Amsterdam area.
They said they were trying to establish whether other people were involved in the alleged abuse of young children up to the age of four.
The man's male partner, 37, has been detained on suspicion of possession of child pornography.
Another employee at a nursery where Robert M, originally from Latvia, worked is also being held. BBC News
