"He's four years old, for God's sake. How can he understand about Covid?"
"I have an idea. Billy ... we need to talk."
"What is it, Mummy?"
"What have Batman, Superman and spider got in common?"
"They all wear masks. Why do you think they do that?"
"So the baddies don't know who they are."
"I s'pose so."
"Look Billy, I don't want you to be scared, but there are baddies at school."
"And if they know who you are, they know who your Mummy and Daddy are, and they might want to hurt us."
"Don't want the baddies to get you, Mummy."
"That's why you have to keep your mask on in school. Do you understand?"
"Do I get to wear a superhero suit?"
"S'pose so. Now go get your mask."
"How'd it go?"
"Okay. But I think I just gave him permission to wear his superhero PJs to school."