At least 30 detainees at the Yarl's Wood detention centre have been on hunger strike since Monday in protest at poor conditions at the Bedfordshire site.
Melchior Singo, 39, from Malawi, said people in the family unit had stopped eating in protest at the sub-standard healthcare and the detention of children. The action began on Monday.
One detainee, Solomom Ojeheonmon, said: "Children, some of them as young as five months old, in this detention centre, are sick."
In April, Sir Al Aynsley-Green, the children's commissioner, said the government's policy of holding 2,000 children a year in removal centres could be harmful to their health. "The UK should not be detaining any child who has had an unsuccessful asylum claim," he said.
Susanna Kushaba, from Uganda, raised concerns when her five-month-old baby developed a temperature. She claims staff ignored her and she was forced to dial 999 to gain medical attention. "I tried telling the staff and the staff were calling the healthcare but no one was coming."
Dr Frank Arnold, clinical director of Medical Justice, said: "We are not at all surprised by these complaints." He said he agreed with MP Alistair Burt, who described Yarl's Wood as "beyond comprehension and decency".