Detectives from British Transport Police are appealing for information following an incident on the Bakerloo Line.
The incident happened on board a southbound service on 3 June at approximately 8.55pm. A woman on board a train witnessed a man acting in an inappropriate manner with a child.
The incident happened between Maida Vale and Edgware Road stations.
Detectives investigating this incident are looking to speak with anyone who was on board a southbound Bakerloo Line train at this time and saw what happened.
If you saw a man act in an inappropriate way towards a child, then please get in touch as a matter of urgency.
You can contact BTP by sending a text to 61016 or by calling 0800 40 50 40 quoting reference 328 of 13/06/2018. Alternatively, contact Crimestoppers on 0800 555 111.
A man has been arrested in connection with this incident, he has been released on police bail whilst further enquiries continue.