This is the following excerpt from the British Embassy in Santo Domingo website:
http://www.britishembassy.gov.uk/ser...=1168350332874
Travelling with children
Following further clarification from the Dominican Republic authorities, we understand that visitors under 18 travelling to the Dominican Republic do not require written authorisation from their parents as long as they enter and leave with the same person/people.
If visitors between the ages of 13 and 18 are travelling alone, or with a group with no one over 18, then similarly parental authorisation is not required as long as the composition of the party is the same on entry and exit. If visitors under 18 do not intend to leave the Dominican Republic with the same person/people that they entered with, then they are required to carry a sworn affidavit drawn up by a solicitor and signed by their parents/legal guardian authorising that. This affidavit needs to be legalised by the FCO and the Dominican Republic Embassy (contact details above). You should contact the Dominican Republic Embassy if you have any queries about these requirements
Hope that clears it up for you.
Marlie