Former first lady Michelle Obama has revealed her passion in the White House was always children and said letting them know 'you are worth it' could change a kid's life.

Michelle became emotional on Friday as she spoke candidly about her work as first lady and how she balanced being a mother to Malia, 19, and 17-year-old Sasha.

'Kids watch what you do, not what you say. So the biggest thing that Barack and I could ever do to be good parents to our kids, is to be good people in the world for them to see everyday.

'They just want somebody to love them. They just want somebody to tell them that they're OK,' said Michelle, who has condemned the Trump administration for separating immigrant families at the US-Mexico border.

Former first lady Michelle Obama reveals her passion in the White House was children and said letting them know 'you are worth it' could change a kid's life. She spoke with Librarian of Congress Dr Carla Hayden (right) at the American Library Association conference

Michelle became emotional on Friday as she spoke candidly about her work as first lady and how she balanced being a mother to Malia, 19, and 17-year-old Sasha

'Kids watch what you do, not what you say. So the biggest thing that Barack and I could ever do to be good parents to our kids, is to be good people in the world for them to see everyday.' The former first family pictured in December 2014

'And that's one of the things I tried to do as first lady with kids and why I did so much with kids because I always thought, this is the interaction that could change a kid's life. This one hug, this one "you are worth it". You never know what can make a difference,' she added.

Michelle made the remarks as she helped kick off the American Library Association's annual conference in New Orleans.

Librarian of Congress Dr Carla Hayden moderated a conversation with Michelle before an estimated crowd of 8,000 inside the city's convention center.

Michelle shared snippets from her memoir, Becoming, including the experiences that have shaped her, from her childhood on the South Side of Chicago to her years as an executive and her time at the White House.

She revealed how former president Barack Obama was not welcome at parent-teacher conferences after he once dropped by Malia's school with a fleet of Secret Service agents.

'I tell this story of how Barack went to a parent-teacher conference, and you know, he’s got a big motorcade. It’s big. And men with guns — machine guns — and black sniper gear, they follow him everywhere in trucks and they’re leaning out, looking at you like, "I will kill you" because that’s their job,' Michelle said.

'But when they’re… on the roof of the elementary school, even Malia was like, "Dad come on." So everybody was sort of, OK when dad didn’t go. Sort of politely going, "Dad you don’t have to come to the Fall-Winter concert. It’s OK. You can take a pass."'

Michelle also spoke about how living in the White House affected their daughter's lives.

She revealed how former president Barack Obama was not welcome at parent-teacher conferences after he once dropped by Malia's school with a fleet of Secret Service agents. The family pictured in October 2013

Michelle also said it was difficult for the former first daughters to go to prom

'You’re trying to be a normal parent in the midst of it when your kid is invited over for a sleepover, and you have to explain to them, "We’ll need your social security number, and there will be dogs sweeping your house and they’re going to ask you if you have guns and drugs and you’ll have to tell them, "Sorry, Julia’s mom but this is what it means to have Sasha over. But it’s going to be fine."'

Michelle also said it was difficult for the former first daughters to go to prom.

'Our daughters had their own detail all the time, so imagine trying to go to prom with eight men with guns and doing anything else you’re trying to do as a teenager,' she said.

'Barack and I were very happy about it. But we had to learn how to discipline them without letting them think their agents told on them,' she joked.

'I had to lie a little bit about where I got my information from. "How did I know that [there was] no parent at that party? Uh, Julia’s mom called me and told me,"' Michelle added.

But when it comes to parenting, Michelle talked about how she learned that 'kids don't need that much'.

'If they know you love them, unconditionally, you can live in the White House, you can live the little bitty apartment that I grew up in. Home is what you make of it. It doesn't have to be perfect. It can be broken and funny and odd in many ways,' she said.

Last week, Michelle joined all of the living, former first ladies in an unusual united political front expressing horror at children separated from their parents at the US-Mexico border under the Trump administration

A few days later President Donald Trump signed an executive order ending family separation at the border. Pictured are dozens of children held inside a US Customs and Border Protection facility

The Trump administration says that nearly 500 children have been reunited with their families. But that still leaves more than 1,800 who remain separated from their parents

'Kids are resilient. They make it through, which is why I think about all the kids that don't make it through because it takes a lot to break a kid.

'But there's so many broken kids which reminds us how bad we're doing because you have to do really messed up stuff to kids to send them off.

'They have to come from a brokenness that is so deep and off and we have to see that in our children and understand that when kids act out there's a reason for it.

'There's no such things as bad kids,' she said to an applauding audience.

Michelle's book is being released in November.

The conference, which ends Tuesday, is expected to draw more than 15,000 participants.

Last week, Michelle joined all of the living, former first ladies in an unusual united political front expressing horror at children separated from their parents at the US-Mexico border.

As Michelle put it on Twitter, in support of Laura Bush: 'Sometimes truth transcends party.'

Michelle wrote those words as she re-tweeted Bush, who first spoke out in an opinion piece Sunday in The Washington Post.

The pair were later followed by Rosalynn Carter and Hillary Clinton.

A few days later President Donald Trump signed an executive order ending family separation at the border.

The president, in an abrupt U-turn on the divisive policy put into place by his own administration, directed the Department of Homeland Security to detain families together so long as children are not put into danger.

'I didn't like the sight or the feeling of families being separated,' the president stated on Wednesday.

Trump indicated that lobbying from his daughter Ivanka, who showed him pictures of the caged and kenneled children, and wife Melania had caused him to have a change in position.

'Ivanka feels very strongly about it. My wife feels very strongly about it. I feel very strongly about it. I think anybody with a heart would feel very strongly about it,' he said.

The Trump administration says that nearly 500 children have been reunited with their families.

But that still leaves more than 1,800 who remain separated from their parents.