The mother of Julian Cadman, the little boy tragically killed in the Barcelona terror attack, has spoken for the first time.

Jom Cadman told News Corp she doesn't sleep and missed her seven-year-old boy "every hour" since the horror attack claimed Julian's life in August.

She was left hospitalised in a critical condition when they were caught up in the chaos on the popular tourist spot Las Ramblas.

Julian and his mother were on holidays when the attack occured.

Ms Cadman, 43, said she loved being a mum "but it's all gone.

"Julian was a blessing, who brought so much joy to our family," she said. “We have to try to be positive, to take one day at a time but I know life will never be the same.

Julian was known as a fun-loving little boy.

“I just want Julian back, I don’t know why I survived and he didn’t."

Ms Cadman said she was holding Julian's hand when he was ripped from her during the attack.

"He had such a lovely day and I had bought him a toy and torch because he had been such a good boy when we came out of the shop and he was snatched from me," she said.

“I don’t remember much, apart from the doorstep of the toy shop. Someone came to help me but I told them ‘I have a boy, he’s in white, please find him.’

CCTV of the attackers before their rampage through Las Ramblas.

Flowers and candles are placed in tribute to victims of the terrorist attack in Las Ramblas boulevard in Barcelona. (AAP)

“I’ve have had a lot of surgery, all of it in Spain, but it doesn’t hurt one bit.

“The biggest pain is in my heart; I want him [Julian] back."

Ms Cadman was confined to a hospital in Barcelona for the first three weeks after the attack where she underwent three rounds of extensive surgery to fix her shattered legs and pelvis.

She returned to Sydney on September 6 and was able to farewell her son at St Patrick's Cathedral in Parramatta on November 4.