A good source of ideas can be found on
www.bsca.org.uk. Click on to Awards section and go thro' Introduction, and pp1-4. I've got kids through bronze, silver and gold Trix stages, but can't do them all myself. Gold level they usually figure out for themselves with some advice from me, tho' it takes much longer than bronze and silver.
Our kids club covers circuit, TT, 'cross, mtb x-country, grass and hard track racing and hill climb TTs. Ages range from 5 - 15. We're fortunate enough to have an 950yard tarmc circuit, two all-weather socccer pitches and grassy areas to meet on.
Happy to discuss details either on-forum or by private email. I appreciate that conditions vary between UK and US, but basic principles remain the same, on or off-road.