Does a wommen need to be Tznius in front of a boy under the age 13? For example can a married women uncover her hair I front of a 10 year old boy?
There is a similar discussion brought down in Yalkut Yosef (Dinei Chinuch Katan page 334) and Rav Shlomo Zalman Auerbach (Sefer Hilchot bat Yisrael Perek 7 Seif 19) that a women shouldn't bring her son who is over 3 or 4 years to a beach that is only for women (we are assuming that this is a non tzniut beach). The Chazon Ish was also asked this question (about the beach), and he said that if the son can remember the time he went to a non tzniut beach, one should not go. Therefore we can conclude from here that a women needs to be modest/tzanua in front of a boy after he is 3 or 4 years old.