Elementary school student's riddle leaves Road to Olympia contestants 'frozen'

In the program Road to Olympia broadcast on July 15, 2018, contestant Kien Giang received the following question in the Finish Line competition: "A family has 6 sons, each son has a sister. So how many people are there in the family?".

A lot of answers were given but no one got it right. If you can find the correct answer in a short time, you are definitely a smart person.

This question requires players to have flexible thinking and quick judgment. Give your answer in the comments section and see how many people think the same as you.