Is the money fully in your control at the moment - no joint signatures etc? At 12, I'd have thought he is well old enough to know how much is there, and to play a part in discussions around how it should be spent. Bear in mind that it is very likely that 3rd level fees will be reinstated by the time he reaches college age.
You need to work out how long you are prepared to lock some/all of the money away for and whether you are prepared to risk some of the capital in order to maximise your investment return.. If you can lock some of it away for 5 years (e.g. his college fund), you will be able to get a better rate over this period.