Thanks for your suggestions.
I'm now thinking some pasta sauce jars have small tops to them - they might do, and I agree that children can handle delicate items if properly taught.
Plastic bottles are interesting - we made bird feeders with them last term - the severed neck could be placed upside down into the bottle base, giving the bulb a 'soft seat'....
Good tip about the charcoal in the water, wouldn't have thought of that - we must have some in school I could acquire...
I'm using non forced bulbs picked up at Lidl today - they have some good bulbs in at a good price.
Thanks again