The eatwell plate is the way the Food Standards Agency talks about food groups, and it is widely used in schools. It is used in Fit for a King.
The official site can be found at http://www.eatwell.gov.uk/healthydiet/eatwellplate/.
There is also a series of useful podcasts by the British Nutrition Foundation. These are probably too advanced for your class, but could help you if you needed more information. This is this first in the series:
