What age are we talking about.
Can they identify the crops from the leaves. How many different crops can they identify,
How many different insects can they see, Bees, wasps, hoverflies, etc etc caterpillars, cabbage white. Pollen beetles, courgettes always attract pollen beetles. Slugs and snails.
What is in the soil? If they put a small amount of soil in water and shake it up then it will separate. Better ask teachers about this since they might need safety specs etc.
The different between earthworms and compost worms.
Making compost. What goes into the compost and what comes out the bottom.
Pests. Can they find holes in the leaves what is eating them.
Fertiliser PKN. What do plants need to grow?
Garden organic have some nice resources, eg what can we compost games. Yes no
https://www.gardenorganic.org.uk/schoolsLadybirds what do they eat? They do not eat leaves so what do they eat, can the children find aphids.