The footage, taken from outside a corner shop at the junction of Smawthorne Grove and Willow Road, shows a middle-aged man with short hair, wearing light grey trousers and a dark blue t-shirt.
Police are keen to talk to the man, who was outside the shop at around at 5.36pm on Saturday, May 31.
Detective inspector Mark Catney, from Wakefield District CID, said: “We know the two victims were at the corner shop around the same time and I believe this man may have seen the two children shortly before the assaults took place on Saturday evening.
“I would ask him to come forward as he may hold vital information which could assist the investigation. I would also ask anyone who recognises the man to contact police.”
Around 90 minutes later, two local girls aged five and six were sexually assaulted as they played on an area of wasteland at the back of Garden Street.
A second incident occurred the next day between 1.20pm and 3.20pm, when two girls aged six and seven were playing in a park near Barnes Road in the Half Acres area of Castleford.
They were approached by a man walking a dog who engaged them in conversation before assaulting the six-year-old.
The man is described as a white male aged 25 to 35 years old with light coloured, short hair.
Two 27-year-old men were arrested in connection with the incidents and remain on police bail.
Det insp Catney added: “The response we have received from local residents has been really encouraging and I would like to thank them for their support while the investigation continues to progress.
“In the meantime, specially trained officers are continuing to support the families of the victims and neighbourhood officers have increased patrols across the area and are visiting local schools to promote safety messages around children not talking to strangers.”
Anyone with information should call Wakefield District CID via 101, quoting reference number 1101 from June 1.