Conkers.
I do hope you consider Health & Safety when allowing children to collect conkers.
If collecting from the ground, hard hats are essential to protect from falling items, kevlar gloves are also required to prevent being spiked by an immature conker. As contact with soil is inevitable, tetanus injections are mandatory.
If missile are use to loosen the conkers, eye protection and body armour is the order of the day.
The area should also be cordoned of to prevent members of the public being injured by flying debris.
You could of course negate the need for any of this by collecting them yourself and giving them to the waiting hoards.
BUT !!
Are you covered for any injuries that may ensue from the use or ingestion of the items, supplying a H&S notice with each one would be a wise precaution along with third party insurance.
What did do before H&S, we had fun !!!
I can remember staying at Pontins many years ago, a conker match for the kids was suggested. Not long before the Dads took over, way overran the allotted time and upset the rest of the weeks schedule. AND, next morning Dads appeared at breakfast with slings, bandages and ice-packs.
If we had had H&S then what excitement those big kids would have missed