"They're Busy" joke

One day, the phone rang, and a little boy answered.
"May I speak to your parents?"
"They're busy."
"Oh. Is anybody else there?"
"The police."
"Can I speak to them?"
"They're busy."
"Oh. Is anybody else there?"
"The firemen."
"Can I speak to them?"
"They're busy."
"So let me get this straight - your parents, the police, and the firemen are there, but they're all busy? What are they doing?"
"Looking for me."