She said she believed her daughter would have found it on a chair.

"I am really angry and sickened ... I haven’t slept. I have been feeling overwhelmingly guilty for taking her there in the first place," she said.

After leaving the restaurant and contacting their local doctor, the family was told to return to the restaurant, get the condom and bring it to the hospital for testing.

However, the mother said McDonald's staff refused to give the condom back.

"What if there is an STD there and my daughter is going to get it? We have to wait two months to do a blood test on her," she said.

A McDonald's spokesperson told WAtoday the franchise was conducting an investigation on the incident.

It is understood a restaurant employee took the condom to the hospital.

“We are very sorry that the incident occurred, and take situations like this seriously," they said.

"Cleanliness and safety are our top priorities and we ensure the shift manager on duty conducts what we refer to as a travel path every 30 minutes.

"The travel path sees the shift manager walk through and check all areas of the restaurant.”