Two mothers inside a Melbourne immigration detention centre say they are being denied appropriate baby food for their children, and one was prevented from receiving some from a visitor on Wednesday.

Huyen Tran and Priya are housed under guard in a section of Melbourne’s immigration detention facility.

Tran lives alone in her unit with her nine-month-old daughter, Isabella, who has lived inside detention since she was born.

Priya, her husband, Nades, and their Australian-born daughters, Kopika, three, and Tharunicaa, two, have been in detention since March, when they were taken from their home in Biloela by Australian Border Force officers in a dawn raid because Priya’s bridging visa had expired.

Under changing visitor rules, food brought in for detainees cannot be food that needs refrigeration, and it must show an expiry date.

Packaged baby food is allowed and Tran has received food from visitors before. However, in recent days food brought by Tran’s husband and other visitors has been turned away.

During a personal visit on Wednesday with Rebekah Holt, a freelance journalist, a Serco guard approached Tran and said she could not take the baby food back to her unit.

When Tran asked why, she was told it was an order from Australian Border Force, Holt said.

Tran told Holt that guards who had previously supplied food for Isabella had stopped.

“They don’t bring me food for the baby,” she said. “I am very worried.”

Australian Border Force said it “strongly rejects claims that children in residential accommodation are not provided adequate, age-appropriate food” and that all necessary steps were taken to care for children in the facilities.

“Detainees are able to receive food from visitors as long as it complies with the outside food policy. The policy is in place to maintain food safety standards and to prevent contraband entering detention facilities concealed in food items.”

Tran told Guardian Australia that Australian Border Force officers had told her on Thursday morning she was allowed to take the food, but did not explain why she had been prevented all week.

“Always they play games with me,” she said. “If I can’t eat, no problem. But my baby needs to eat.”

Priya said it was very difficult to get fresh food in detention, and her two-year-old was showing dental problems and vitamin deficiencies.

“My baby likes fresh grapes and avocado,” she said. “But in the centre the baby is not eating.”

Tran and Isabella are not permitted to live in the community with Tran’s husband, who lives in Australia on a 457 working visa and is unable to sponsor his wife.

“This is exactly why children should not be in detention,” said a human rights lawyer, Alison Battisson.

“For precisely reasons such as this, international legal protections were put in place to prevent children being raised in detention centres … Article 2 in fact, [in] the convention on the rights of the child, provides that children should not be punished for the status of this parents.”

Battisson noted two reports on the issue by the Australian Human Rights Commission in 2004 and 2014.

“It is ridiculous that children are still being detained, when the adverse consequences are known,” she said.

“Regardless of the best will of the detaining authorities, closed detention is not a suitable environment to raise children in, particularly infants.”

The department said Tran and Isabella were “housed in an alternative place of detention”, in a “residential-style facility”.

A United Nations body has been examining whether Australia is breaching its human rights obligations by holding Isabella in arbitrary detention.

“The government submission argues that Isabella is a ‘guest’ in detention,” said Battisson. “This response prioritises Australian border control policies over the rights of a single infant. This is not a proportionate application of Australian policy.”

The Greens senator Nick McKim said it was “outrageous” the mothers were being prevented from receiving baby food.

“The minister has a duty of care over everyone in there, including children and ensuring they have adequate nutrition. He needs to step in and intervene and make sure they get the food they need to stay.”