Regarding the query – ‘life-jackets or buoyancy aid’ – it seems generally accepted that buoyancy aids are more appropriate for all forms of dinghy sailing. Basically they are less bulky, provide immediate support when in the water, and provide additional thermal insulation. Chandlers offer a full selection including children’s sizes.
For general advice on independent sailing there is a very useful (and authoritative) publication from the RNLI called ‘Dinghy Sailing – Sea Safety Guidelines’ which can be obtained free from their web-site or phone 0800 3280 600