'All I ever want is justice for my child - what have I done wrong?' asked Jiang Yalin , 35, whose three-year-old daughter suffers from kidney problems from drinking melamine-tainted milk powder since birth. Doctors found several stones in her daughter's kidneys, and the toddler's face often puffs up from the fluid build-up in her body. Jiang and other parents seeking medical treatment and compensation have travelled to Beijing several times to petition the central government, becoming targets of police surveillance every time. And when police in their community found out about their plans, they were taken into police custody to stop them from going to Beijing. 'Even when I went to Guizhou to see my parents, the local agents followed me,' Jiang said. 'But I'm not doing anything illegal!' Jiang's daughter was one of nearly 300,000 children who fell ill from drinking milk tainted with melamine, a toxic industrial chemical. The scandal, which saw the death of six babies, caused a national furore when it was uncovered in 2008. In all, 21 people were convicted over the scandal and two - a dairy farmer and a milk salesman - were executed. Parents blame repeat cases this year on complaints having been silenced while people they hold responsible - corrupt officials who turned a blind eye to malpractice - have not received the punishment they deserved. The former head of the General Administration of Quality Supervision, Inspection and Quarantine, Li Changjiang, who was forced to step down over the scandal in 2008, was appointed deputy chairman of a high-profile working group on combating online pornography just 15 months after his resignation. Another official at the national quality watchdog who had to step down was also given a new job. But parent representative Zhao Lianhai has been in custody since November charged with 'provoking quarrels and making trouble'. In May, the father of a one-year-old boy who died of respiratory and urinary system failure was given 're-education by labour' detention for a year for voicing his anger on the internet. Many lawsuits brought by parents have been rejected by courts. 'If victims could seek justice from a fair and open legal system and the perpetrators were properly punished ... this wouldn't happen,' said a father from Zhengzhou whose child is suffering from kidney stones.