What is the exact age of Tamiz (التمییز) for children?

I have heard that it is better for men and women to observe some items or rulings (Ahkam) in front of the children who are at the age of Tamiz (التمییز). According to my researches, the age of Tamiz is the age of the children who are not in the age of Bolugh (puberty) but are able to realize the difference between good and bad things. - www.askdin.com But I did not find any precise number (age) about it. So what is the range of Tamiz age?