Human trafficking is a process that is a combination of three basic components:
Movement - (including within the UK - referred to as Internal trafficking) recruitment, transportation, transfer, harbouring or receipt of persons.
Control - threat, use of force, coercion, abduction, fraud, deception, abuse of power or vulnerability, or the giving of payments or benefits to a person in control of the victim
Purpose - exploitation of a person, which includes prostitution and other sexual exploitation, forced labour, slavery or similar practices, and the removal of organs
An international definition for trafficking contained in article 3 of the UN Palermo Protocol to Prevent, Suppress and Punish Trafficking in Persons, Especially Women and Children, supplementing the UN Convention Against Transnational Organisational Crime has now been widely accepted across the world as the basis for identifying and working with the victims of trafficking:
(a)"Trafficking of persons" shall mean the recruitment, transportation, transfer, harbouring or receipt of persons, by means of the threat or use of force or other forms of coercion, of abduction, of fraud, of deception of the abuse of power or of a position of vulnerability or of the giving or receiving of payments or benefits to obtain the consent of a person having control over another person, for the purpose of exploitation. Exploitation shall include, at a minimum, the exploitation of the prostitution of others or other forms of sexual exploitation, forced labour or services, slavery or practices similar to slavery, servitude or the removal of organs.
(b)The consent of a victim of trafficking in persons to the intended exploitation set forth in sub-paragraph (a) of this article shall be irrelevant where any of the means set forth in sub-paragraph (a) have been used.
(c)The recruitment, transportation, transfer, harbouring or receipt of a child for the purpose of exploitation shall be considered "trafficking in persons" even if this does not involve any of the means set forth in subparagraph (a) of this article
(d)"Child" shall mean any person under eighteen years of age
Article 6(4) focuses on the support provided to victims of trafficking stating that:
Each state party shall take into account, in applying the provisions of this article, the age, gender and special needs of victims of trafficking in persons, in particular the special needs of children, including appropriate housing, education and care.
The Palermo Protocol establishes children as a special case and any child found to have been moved for exploitation is considered to be a victim of trafficking, whether or not they have been deceived, or agreed to move, because it is not considered possible for children to give informed consent, as set out in paragraph 5 above. The distinction between trafficking and smuggling is also considered an important one in determining if a child has been trafficked, as smuggling is taken to mean that arrangements are consensual and that a smuggler has been paid to help people to enter the country illegally, after which there is no longer a relationship and no exploitation. However, there are concerns that in respect of child and adult victims of trafficking, and at the front line of child care and protection work, the distinction between trafficking and smuggling is often blurred - research has highlighted that some children have been abused on their journeys to Scotland after paying smugglers to get them to the UK. 
The UN High Commissioner for Human Rights also recognises that trafficked children have specific needs as a consequence of age:
Children who are victims of trafficking shall be identified as such. Their best interests shall be considered paramount at all time. Child victims of trafficking shall be provided with appropriate assistance and protection. Full account shall be taken of their special vulnerabilities and needs ( UNHCHR 2002, principle 10)