Police are searching for a middle-aged man who sexually assaulted two young children he took from a Perth school holiday care program.

Key points: Two young children taken from a North Perth childcare facility and sexually assaulted

Two young children taken from a North Perth childcare facility and sexually assaulted The children were enticed away by a middle-aged man

The children were enticed away by a middle-aged man They were found in Hyde Park

The four-year-old girl and five-year-old boy walked off yesterday morning with an unknown man from the care program in North Perth, which is held in a community hall.

Police said the man took them to a nearby location where he sexually assaulted them, then left them in Hyde Park.

A woman found the pair, who are not related, at a playground about 12:15pm, but police said the childcare centre had not realised they were missing.

The man being sought is described as being in his late 40s to late 50s with pale skin and short greying hair, wearing an oversized black jacket, black trousers and a business shirt.

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An email sent to families from the holiday program provider said extra staff had been employed to provide extra supervision at the centre.

"I would like to inform you and make everyone aware that two children were taken from the centre yesterday and an incident occurred which is now under police investigation," the email said.

"Both children are safe and at home with their parents."

Police commander Kylie Whitely said it was "every parent's worst nightmare".

"He lured and enticed them out of the centre," she said. "It's a delicate situation ... a very serious incident."

She said the parents of the children were "very distressed".

Police did not know what the man had used to persuade the children to walk off with him.

"They've been enticed out of the centre so [they were] obviously offered something that is going to entice two young children," Commander Whitely said.

A manager at the holiday care said the centre would not be commenting while the police investigation was ongoing.