New South Wales police believe a man who kissed a four-year-old boy at a McDonald's restaurant in Sydney's inner west kissed a second boy at another takeaway outlet within a few hours of the first incident.

Police say they have extensive CCTV footage of the man they believe is responsible for the alleged aggravated indecent assaults.

They have also released an image of the man and are seeking public help to find him.

The first incident happened at a McDonald's outlet in the inner western suburb of Drummoyne about 8:30pm, when a man kissed a four-year-old boy on the lips before handing him a lollipop.

The lollipop is now part of a forensic investigation as police seek information from any diners at the restaurant who may have witnessed what happened.

The man fled the restaurant in a small white hatchback vehicle, believed to be a Hyundai Getz or similar, with yellow and black number plates.

Detective Chief Inspector Glen Fitzgerald says it was a very brazen attack.

"Whilst at the restaurant the mother has gone to order some food at the counter and whilst that has happened a male that we would describe as between the ages of 45 and 55 years of age has approached the young four-year-old boy, held him by the face and given him a prolonged kiss," he said.

"After doing so he handed the boy a lollipop and immediately left the store."

The second incident occurred about 10.20pm at a fast food restaurant on the Princes Highway at Sylvania in Sydney's south.

A woman with her daughter and son entered the store and all three went to the toilet.

While in the men's toilet the 11-year-old boy alleges a man touched him inappropriately and kissed him on the mouth.

The man threatened the boy not to tell anyone before running from the store.

The boy immediately informed his mother and the store.

Police were later contacted by the family.

CCTV footage of both incidents shows a man aged between 45 and 55, who is about 170 centimetres tall and wearing distinct square-rim glasses.

The man is also seen wearing a blue baseball hat, blue shirt and pants and carrying a shoulder bag.