Raja Hussain, 10, still sees flood waters roaring towards his farming village most nights. They sound like a high-speed train.

Monsoon floods hit Pakistan six months ago. Yet, those vivid images still haunt the Pakistani child's nightmares.

"In the dreams I see myself praying to Allah for help," said Hussain.

One of the worst natural disasters in Pakistan's history left about 11 million people homeless, killed nearly 2,000, destroyed millions of acres of crops and hammered the economy.

They also inflicted a heavy psychological toll, and children are most vulnerable.

A study by Save the Children showed that 87 percent of children interviewed were stressed and aggressive, 75 percent could not express themselves properly and 70 percent felt insecure, with fear of people, water, open places and darkness.

In Mir Hassan in Sindh province in the south, which was hardest hit by the floods, aid workers attempt to bring psychological stability to children.

The idea is to erase disturbing memories by engaging them in games, or having them draw images of the most frightening part of the floods so they can come to terms with it. It's called psycho-social counselling

Some children, as well as adults, have trouble sleeping because of the trauma.

"If you don't sleep for several days you can suffer from psychosis," said Ea Suzanne Akasha, of the Danish Red Cross, who heads a psycho-social unit.

"People start imagining they are seeing crocodiles and things coming out of walls."

Battling the widespread stigma attached to mental illness can make the task even more challenging. Some of those mentally disturbed by the floods are tied to trees or chairs in villages.

During one psycho-social session in Mir Hassan, a Pakistan Red Crescent volunteer throws a soccer ball at a group of boys, each one calling out his name as he catches it. Others play cricket in the dirt.

Villagers crouch nearby in front of a wall that was submerged under 15 feet (4 metres) of water during the floods. They watch the activities across a canal of thick, green stinking water.

Memories of people frantically escaping the floods, and waters rising to her knees, still terrify six-year-old Fawzia Ali Siyal. She takes part in the fun and games, but also keeps an eye out for her eight-year-old sister, who has also been traumatised by the floods.

"When my older sister thinks of the floods she weeps," said Fawzia. "I tell her 'don't worry. It will be fine'."

Teenagers are also struggling to cope. Fifteen-year-old Safraz Shahnawaz has become anti-social and is frequently angry, for no reason. "I often see ghosts when I sleep," he said. "They have angry faces."

Up to seven million people remain displaced by the floods, said Save the Children. Many who managed to return to their villages have few means to make money to rebuild homes or resume their children's education, depending mostly on aid groups.

"There is an urgent need to get children and their families back into proper homes and schools so they can start to live a normal life again," said Save the Children.

Raja Hussaid said he wants to be an electrical engineer as he proudly held schoolbooks, one of the lucky few who is learning again. But it doesn't take much to revive his anxieties.

"Sometimes I hear my teachers sitting together and talking about the floods," he said nervously.

Aid workers are confident they can help, despite the deep psychological scars. Young boys gather in a crowd taking turns singing songs, some of them joking that the floods may have prepared them for other traumas later in life.

"Allah protect me so that my love doesn't leave me," one boy sang, as others giggled.