The incident happened in Oakmere Park, off Highview Gardens, between 11.50am and 12.20pm on Monday (October 9).
The child was in the playground area with her mother when she attempted to climb the ladder on the slide.
A man then approached the girl and placed his hands on either side of her torso, before her mother quickly intervened.
The man has been described as aged in his 40s, wearing navy tracksuit bottoms with a hoody tied around his waist, and socks with sliders on his feet.
The suspect proceeded to loiter nearby while on his phone, with the victim and her mother leaving the park shortly after. The child suffered no physical injuries during the incident.
“This was an unsettling incident for the victim and her mother, and has left them feeling understandably shaken,” said Inspector Rachael Robertson, who leads the Hertsmere Safer Neighbourhood Team.
“I want to reassure the community that we are doing all we can to trace this man, and to understand what his intentions were.
“The incident happened at a time when there were likely to be other people in the park, so we are appealing to anyone who thinks they may have seen this man or witnessed what happened to please come forward and speak to us as soon as possible, quoting crime reference 41/81092/23.
“In the meantime, we have increased our patrols of the park so the community will see an increased police presence in the area.”
Anyone with information can contact PC Harknett at [email protected].
You can report information online at herts.police.uk/report, via online web chat at herts.police.uk/contact, or by calling the non-emergency number 101, quoting crime reference 41/81092/23
Alternatively, contact Crimestoppers anonymously on 0800 555 111 or online at crimestoppers-uk.org.