Children crawled through a fence and chanted "we need your help" at a controversy-hit migrant centre last weekend, according to a support group.
SOAS Detainee Support (SDS) visited the Manston site in Kent on Sunday, where 700 new people were moved to after a petrol bombing in Dover.
Upon arrival, the group reported seeing children "run away" from security guards ordering them inside, before "crawling through a fence" to be heard.
Concerning footage shows the children chanting "freedom" and "we need your help" while being ushered back to their families.
In a series of tweets, SDS wrote: "Dozens of young children are being held at Manston detention camp in Kent.
"Mothers, fathers, children and babies from Syria, Iraq, Afghanistan, Pakistan and elsewhere. We went today and heard them chanting for their freedom."
People on the site said conditions were "not nice" and that some of them were getting sick, but no doctors or lawyers were on hand to help, according to the group.
Some of them had reportedly been staying there for up to 40 days.
SDS added: "The camp is already overcrowded - and we saw hundreds more people arriving on coaches and buses, exhausted and spent.
"We saw 13 coaches full of people arrive in just 3 hours. Only one coach with a handful of people, including security personnel, left during that time."
Robert Jenrick has insisted the Manston site is "fit for purpose".
Asked about how it could be legal to detain migrants at Manston for more than 24 hours, the immigration minister told Sky News: "We do not have the right to detain anybody for more than 24 hours.
"A site like Manston needs to operate within the law. I have been completely clear to my officials that's what we must do.
"We must ensure that this site returns to not just a legal way of operating but a humane and compassionate way as quickly as possible."
He added that the "root cause" of what is happening at the centre is not the fault of the Government.
Mr Jenrick said: "Conditions are poor. They are improving. We are trying to ensure that as many people as possible leave the site to better accommodation, mostly in hotels, as quickly as possible.
"It is not designed to be somewhere where people stay for a prolonged period of time.
"It is, by necessity, relatively austere. The task now is to ensure it gets back to its normal working pattern."
He also said he was not there to "defend" the situation as he admitted that people had been staying there for over 24 hours and had been sleeping on the floor on mats.
"This is not a satisfactory situation. I'm not here to defend that," he told the programme.
"I would just say that the root cause of what we're seeing at Manston is not the Government.
"It's certainly not the brilliant Border Force Staff who are managing the site, the contractors, the catering staff. The problem is that thousands of people are crossing the Channel illegally every day."
The support group's visit came on the same day that a 66-year-old man launched three home-made explosives towards the Border Force immigration centre in Dover.
Two people inside the centre were hurt during the strike, however they only suffered minor injuries.
It is not yet clear why the attacker targeted the migrant centre, although police are investigating whether he had far-right links.
Lucy Moreton, spokesperson for the Union for Borders, Immigration & Customs, said it was a "really frightening" time for staff working with migrants.
She told BBC Radio 4's Today programme: "There's been a lot of drones flying over the site in the last 24 hours.
"There's a lot of tensions on the site. The migrants are very keen to be moving, to be moved on, to get their freedom back. Staff face, on a daily basis, sitdown protests."
