A man was seen to be riding an e-scooter with a baby strapped to his front on Totteridge Road, towards the Bowerdean crossroads at around 12.20pm on Monday 16 May.
The man is described as white, in his late twenties to early thirties, slim, with short brown hair, wearing jeans and trainers.
Investigating officer, PC Richard Lunn, of the Joint Operations Roads Policing Unit, said:
“We are appealing to anyone who may have witnessed this incident to please come forward.
“You can report information by calling 101 or via the Thames Valley Police website, quoting reference 43220220677.
“Additionally, you can also submit any video such as dash-cam footage via our dedicated portal.
“Alternatively, if you wish to remain anonymous, you can contact the independent charity Crimestoppers via 0800 555 111 or its website.”

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