Police are investigating three allegations of sexual assault of children at a school in Hillingdon.
The allegations - all said to involve children under the age of 13 - were reported to police on April 29.
Officers from the Sexual Offences Exploitation and Child Abuse command are investigating but no arrests have yet been made. Enquiries continue.
A parent, who cannot be named, said police have been conducting interviews since the allegations were made.
He told getwestlondon: "It started with one allegation, then other children came forward about the same suspect.
"I'm worried about the children and hope it can be stopped as soon as possible as there could be other victims."