Why does Theo throw a tantrum every time his parents take him shopping? And how do we protect consumer children from marketing messages?

Théo begs for the same brand shoes as his friend. His mother says no: they’re too expensive. Later, at the supermarket, he absolutely wants the homework book with a superhero on the cover. This time, his mother relents, but when Théo asks for sweets at the counter, she refuses. Why does Théo throw tantrums? And how do we protect consumer children from marketing messages?