Many people, including children, have fled to Britain and are waiting for their families to join them. After Brexit, the situation of child refugee will become more complicated.
For now, there is a common regulation of immigration policies in EU countries. If Britain leaves the European Union, they will no longer need to cooperate with these policies or take any refugees. Hence, children who are desperate to reunite with their family will likely turn to illegal/criminal means to enter Britain, mostly via smugglers who have already caused deadly damage (e.g. last week 39 people died in a lorry on their way to Britain).
Calais (France) is an important spot for refugees departing for Britain by boat. Here, criminal groups exploit children (even sexually) with the promise of passage to the UK. Children are so desperate to join their families they will do anything, including entering indentured servitude, if they cannot pay.
Child protection organizations say Britain should assist in reuniting children with their families. Refugee Youth Service would like to offer legal help, but children do not always cooperate; they choose the faster, seemingly less complicated way to their destination. If they engage in criminal activity however, it is more and more difficult to help them. Additionally, they will arrive to Britain without any record of their identity or whereabouts, and hence, they will have a difficult time accessing health care, education and employment in the future.