Her father-in-law Tony Cadman said Ms Cadman is in a serious but stable condition in hospital, but his grandson is missing.
"We have found Jom (his mum, my cousin-in-law) and she is in a serious but stable condition in hospital".
The appeal concluded: "Please share, especially if you have family or friends in Barcelona".
The boy's concerned aunt Maricar Querimit Estera, posted onto Facebook saying "pray for my nephew who [is] still missing in Barcelona attack. your family [is] waiting for you".
An Australian government spokesperson said one citizen remains unaccounted for and three were injured.
Meanwhile, US president Donald Trump wrote on Twitter: "The United States condemns the terror attack in Barcelona, Spain, and will do whatever is necessary to help".
Mapped: US and Allied Missile Defenses Against North Korea
The confirmation came as NBC News in the U.S. gave details on a possible pre-emptive United States military strike on North Korea. Resident Isaac Camacho, 19, says he feels Guam's relationship with the US mainland is "a little misunderstood on their part".
Two New South Wales women are in hospital, while two Victorian men - both of whom were hit by the attacker's van - have been discharged after receiving treatment.
A 3-year-old Spanish boy and his mom were among the 13 killed when a terrorist van slammed into pedestrians in Barcelona, according to reports Friday.
A five-year-old Irish boy was also injured, suffering a broken leg, officials in Dublin said.
Julian was born in Britain, but moved to Australia when he was three, the newspaper reports.
Australian Gil Van Der Venne also witnessed the attack unfold from his hotel balcony.
Ireland's foreign affairs minister, Simon Coveney, said: "In a way it's a miracle that more Irish people weren't involved, given that there are so many Irish people in Spain, Barcelona and Cambrils at this time of year".
"Our prayers are with Suria and all others affected by this tragedy", the spokesperson said.
The Queen said in her message to King Felipe: 'Prince Philip and I send our honest condolences to Your Majesty, and the people of Spain, following the awful terrorist attacks in Barcelona and Cambrils which killed and seriously injured many.