Essex Police are investigating several incidents of a man taking dummies out of babies’ mouths.
Four such incidents were reported around Harlow between 10 February and 7 August.
A child was also assaulted on one occasion.
The suspect is described as slim, white, and aged in his 20s, with light brown eyes and yellow teeth.
Police have released an image of a man they would like to speak to in connection with the incidents.
The picture, which was taken from behind, shows a person in a black hooded top and carrying a black Nike bag with a white logo. His face is not shown in the image.
Essex Police have asked anyone who recognises the man, or has seen someone matching the description acting suspiciously, to contact them.
Chief Inspector Paul Austin, district commander for Harlow, said: “This is a series of unusual incidents and, as a parent myself, I understand the level of concern they will cause.
“However, I want to reassure the people of Harlow that we have detectives dedicated to investigating these incidents, have linked previous incidents, and my teams will be visible out in the community to provide reassurance.
“I would urge you to continue going about your daily business as usual but be vigilant of anyone acting suspiciously.
“I need anyone who has information or recognises this person to contact us.”
