Record numbers of unaccompanied child asylum seekers who arrived in the UK on small boats are being accommodated in four hotels along England’s south coast, a situation that the Children’s Society has described as “shocking”.

About 250 unaccompanied children who arrived in small boats are thought to be accommodated in hotels, which Ofsted said was an unacceptable practice.

In September, Home Office officials told the home affairs select committee it was accommodating 70 unaccompanied children in hotels.

On 23 November the government announced that a scheme for this group of children to be dispersed to different local authorities was temporarily being made mandatory. But individual councils have two weeks to make representations against this new rule. London councils currently care for 1,500 of these children – a third of the total.

Kent county council officials said they were at capacity, caring for 363 unaccompanied child asylum seekers as of 23 November along with 1,071 care leavers.

Children’s and refugee charities say their concern for young refugees’ welfare is mounting as record numbers of adults as well as children continue to arrive in the UK in small boats.

Marieke Widmann, policy and practice adviser at the Children’s Society, said: “These are vulnerable children and young people who have often fled war and persecution and may be frightened and distressed after an unimaginably traumatic journey.

“It’s crucial they get the help, support and security they need when they arrive here alone, including access to appropriate accommodation. Moving unaccompanied children into hotels with limited care and supervision is shocking and places these already vulnerable children at incredible risk. We are aware several children have already gone missing.

“The Home Office has a duty to protect all children and promote their welfare. It must ensure these children receive proper care and support so they feel safe and secure and can recover from the terrible trauma they have been through.”

The question of who is legally responsible for these children has been raised by lawyers. Rebecca Ives, a solicitor at Wilsons, said: “The home secretary is effectively acting as the corporate parent for these children. Central government does not have any statutory powers to act in this way or to accommodate [unaccompanied asylum-seeking children] in hotels.

“We are concerned that the Home Office practice of accommodating unaccompanied asylum seeker children in hotels is removing them from the protections and safeguarding afforded to them under the 1989 Children Act. Some of them will be victims of trafficking and/or torture and therefore particularly vulnerable and at risk.

“It has been stated that these children will only be in hotels for very brief periods whilst alternative arrangements are made, but for some children this period lasts for more than one month.”

Bridget Chapman of Kent Refugee Action Network said: “We were concerned to discover that these unaccompanied asylum seeker children who recently arrived on small boats are being accommodated in hotels on the south coast.

“We have a lot of expertise in supporting these young people and it is our remit to do so. But the Home Office has not contacted us about this. The children are being guarded by security guards. We don’t know if they have enough privacy, if they are being supported by qualified social workers, nor whose jurisdiction they are under.

“Hotels are not suitable places to accommodate these children. Who is checking up on them and how long will they be in the hotels?”

A government spokesperson said: “We are working around the clock with local authorities to seek permanent places for unaccompanied asylum-seeking children across the UK. Our efforts remain focused on ensuring every single unaccompanied child receives appropriate support and care whilst we seek a permanent place for them.

“We are determined to end the use of hotels as soon as possible and our nationality and borders bill will fix the broken asylum system.”