Among them is Yu Lufang of Hangzhou, who for almost three months before the scandal broke in September did not know why her daughter cried every time she urinated.

Then the 36-year-old mother saw the news about the tainted formula on TV and rushed 1-year-old Yu An to a hospital where an ultrasound showed stones in each kidney. The baby repeatedly was given IV fluids, but was not hospitalized for lack of space. Doctors advised Yu to give her daughter more water.

"Now we let her eat only rice and drink water. I don't allow the child to have any dairy products. It has already cast a shadow on us," Yu said.

She said she still worries about possible lingering health problems even though her daughter, an only child, seems much better.

"Now she is playing again and she eats well. But she still can't talk so I don't know if she's in pain or not," Yu said.

Hangzhou authorities told Yu the dairies were offering her 2,000 ($294) yuan for compensation, but she said she turned it down because she wanted her concerns about the future to be addressed.

The government has offered payouts to defuse public anger that it fears could spark unrest. Zhao was detained by Beijing police Jan. 1 apparently to prevent him and other parents from holding a news conference to complain about the proposed compensation scheme. He and four other parents were released after a day.

Three of the signatories are parents whose children died from tainted milk, Zhao said, but it was not clear if their babies are included in the official count.

The Health Ministry did not immediately respond to a faxed list of questions, and calls to the dairy association rang unanswered.