The first Child Trust Funds (CTF) are maturing this month as recipients turn 18.
The scheme, no longer available, was open to children born on or after 1 September 2002.
However, the survey by Orbis Investments found many were not aware of the money coming to them.
Nearly a quarter (23%) of the 16 to 17-year-olds surveyed said they will continue to save the money and a tenth (10%) said they will spend the money once they can access it.
Just under half (44%) said they were unsure what to do with the money. Just over one in ten (12%) of those surveyed said they will opt for a Cash ISA.
Dan Brocklebank, UK director of Orbis Investments, said: “Our survey shows that the majority of teenagers have no idea about the money sitting waiting for them, and some parents may well have forgotten these funds exist.
“Now that those turning 18 are gaining access to their money it is important that they consider all their options including investing, or keeping their pot invested, in order to make the most of the contributions made on their behalf.”
With global equities having fared substantially better than cash over the long-term, Mr Brocklebank said CTF recipients should consider investing their unexpected windfall rather than choosing a Cash ISA.