how about starting to grow some fruit and vegies at home? Strawberries make great snacks for young children and cress is supposed to be a quick way to show kids what can happen if they sow and care for seeds.
It could certainly be a cheep hobby to keep them occupied for a while if they find it interesting, especially if you have a garden.
If the plant growing goes well you might want to have a go at making some compost or a wormery to reduce the costs associated with the plant growing, but I think the best way is to take things one step at a time.