Sheridan, who won three silver Logies for his role in Packed to the Rafters, was preparing for the opening night of Hair the Musical when the attacks occurred about 10.30pm on Friday night in the CBD.

Hair castmate Matthew Manahan was glassed near Murray Street Mall minutes before Sheridan's brother was assaulted in Hay Street Mall.

"If my brother wasn't there, I would've been completely caught unaware," Sheridan posted to Instagram on Saturday.

"I'm in shock, I'd never seen someone so aggressive and so fast."

Sheridan said the same person was responsible for both attacks.

"He had no motive and chose the sweetest people I know to hurt."

Manahan, a graduate of Western Australian Academy of Performing Arts, was taken to Royal Perth Hospital and was released before 8am.

Police are also investigating a third alleged assault when a man in his 20s was punched near the William Street end of Hay Street Mall.

Two boys have been charged over the alleged incidents.

A Swan View boy, 14, faces four charges including aggravated assault occasioning bodily harm and possession of stolen property.

A Northam boy, 15, was charged with five offences including two counts of common assault and carrying an article with intent to cause fear.

Both were due to face Perth Children's Court on Saturday.

Australian Associated Press