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...