The so-called Islamic State (IS) group has said it carried out the attack in Musayyib.
IS has long mounted a violent campaign against Iraqi Shia, denouncing them as heretics.
The group has increased its attacks on civilians in big cities in Iraq as increasingly loses territory.
Its main stronghold of Mosul is expected to be recaptured soon.
A suicide bomber has struck a market in Iraq in a town near the Shia holy city of Karbala, killing at least 20 people.