I have a talk that I deliver to students about the origin of the elements. I have attached the A level version. I can modify it to talk to KS4 students and it fits nicely with the part of the curriculum around life cycles of stars. The A level talk uses some of the equations from the AQA A level physics data sheet.
The talk itself is based on the origin of the elements. Hydrogen helium and trace amounts of lithium were made in the big bang and all the other elements (not quite there is spallation) were made in processes in the interiors of stars.
Part of this talk involves explaining fusion in stars. I have a demonstration that uses balloons to demonstrate beta plus decay and its role in the proton chain. This is a way some star convert hydrogen into helium in their cores.
All the blue elements above were made in fusion processes in the cores of stars.