Two children who were the subject of an Amber Alert in the early morning hours on Thursday were found safe in downtown Toronto, according to police.

York Regional Police said the two young brothers, aged two and four, were found with their grandfather driving down Lake Shore Boulevard around 4:30 a.m. ET.

A Toronto police officer recognized the vehicle described in the alert and pulled them over, said York Regional Police Const. Andy Pattenden.

York police, in consultation with Ontario Provincial Police, issued an Amber Alert for the boys about 90 minutes earlier, around 3 a.m. ET.

"The system once again worked," said Pattenden.

As a direct result of the Amber Alert Mr. Easton and his two grandchildren were located by the Toronto Police Service driving on Lakeshore Blvd in Toronto. They are all in good health. We thank everyone for their assistance. —@YRP

The boys had last been seen with their 70-year-old grandfather at Upper Canada Mall in Newmarket on Wednesday afternoon.

Pattenden described the grandfather as a "vulnerable person" who seemed to be confused when police located him and the boys.

People across the GTA have been calling 911, yet again, to complain about the <a href="https://twitter.com/hashtag/AmberAlert?src=hash&ref_src=twsrc%5Etfw">#AmberAlert</a> notification system. Some of the calls have been abusive and very rude. Meanwhile, <a href="https://twitter.com/YRP?ref_src=twsrc%5Etfw">@YRP</a> Cst. Andy Pattenden says the children were found because of the alert. <a href="https://t.co/NtC7YLkaxa">pic.twitter.com/NtC7YLkaxa</a> —@JeremyCohnTV

York police had initially told media on Wednesday evening that they were not concerned for the trio's safety. Their assessment changed, however, as the night dragged on.

"Things are constantly changing and evolving in an investigation," Pattenden said.

"We have the utmost concern when children are involved."

York police emergency dispatchers received multiple calls overnight from residents angry that the Amber Alert woke them up, Pattenden said.

"We apologize for the inconvenience, but when there are kids' safety at risk, we pull out all the stops and this was just one of the tools that was being used."