Swallow nest destroyed by kids with catapults and chicks killed

Please help, can anyone advise me what can I do…

My friend has swallows nesting in her horse shed, we watched 2 days ago 4 swallow chicks sticking their head out, while parents were busy feeding them. 

To our horror, today we found nest destroyed and chicks killed ! There were couple of traveller’s boys asking my friend about a week ago if there are any birds on her field, but when she spotted boys holding catapults, she told them to keep away from her field.

We suspect these two boys killed swallow chicks. 

Can we report this anywhere, can something be done about this crime ? 

thank you in advance for your help.