Barbara Wilson said she was queuing to order when her grandson, who had been playing with her own son, ran in and said a man had hit him.

She took a manager with her to confront the man who she claimed struck her eight-year-old grandson after he trod on the man’s own two-year-old son.

"I just keep thinking about it, I can’t believe it happened in this day and age," she said.

"I just feel absolutely awful that I couldn’t protect my own grandson in McDonalds on McH-appy Day."

Ms Wilson said she was outraged that a man had meant to harm a child and had never experienced anything like it in her 30 years of living in Bunbury.

"You are not allowed to strike your own child let alone someone else’s," she said.

She believes her grandson accidentally came into contact with the other child while playing.

Too shocked to call the police at the time, she said even if the man was found the family was unlikely to want to press charges as her family was left traumatised.

"The person has scarred my son for life and affected our whole family," she said.

She thanked McD-onalds staff and a woman for their help at the restaurant.