Bachelet, who is the former president of Chile, said in a statement on Monday that even detaining children "for short periods under good conditions can have a serious impact on their health and development.
Bachelet replaced Zeid Raad Al Hussein in August 2018 as the UN human rights chief, Presstv Reported.
"As a pediatrician, but also as a mother and a former head of state, I am deeply shocked that children are forced to sleep on the floor in overcrowded facilities, without access to adequate health care or food, and with poor sanitation conditions," she said.
US President Donald Trump has made his hard-line stance on immigration an integral part of his presidency and has promised to build a wall along the US-Mexican border to curb the flow of migrants from Mexico and Central America.
The Trump administration is facing growing complaints from migrants about severe overcrowding, too little food and other hardships at detention facilities on the US-Mexico border.
A report published last week by Amnesty International said the White House is waging a campaign against activists, journalists and lawyers who support the rights of migrants and asylum seekers and record abuses of immigrants.
On Saturday, the New York Times published an article describing a US border patrol station in Clint, Texas, as filled with hundreds of children wearing dirty clothing and packed into disease-ridden cells.
The UN human rights chief said those who find themselves in these facilities "have embarked on perilous journeys with their children in search of protection and dignity and away from violence and hunger."
"In most of these cases, the migrants and refugees have embarked on perilous journeys with their children in search of protection and dignity and away from violence and hunger," she said.
Bachelet noted that nations have the right to determine their immigration policy and acknowledged the complex challenges surrounding migration management, including in Central America.
"But clearly, border management measures must comply with the State?s human rights obligations and should not be based on narrow policies aimed only at detecting, detaining and expeditiously deporting irregular migrants," she added.