The Shulchan Aruch states that as a general rule, the Torah absolves women from mitzvot that are bound by time (Mitzvot aseh she’ha’zman gerama). Because the Shema must be recited at very specific periods of the day – women are exempt. Nevertheless, it is proper for the women to formally accept upon themselves “Ohl Malchut Shamayim” (the yoke of Divine Kingship) each day, by reciting the first pasuk of the Shema as well as, “Baruch shem kevod malchuto…”
Concerning children: Rabeinu Tam (a”h) was of the opinion that once a child reaches the age of chinuch, (generally ages 6 or 7), depending on the child’s development – the parent must ensure that the child recites Shema at the proper time each day and night. Before this age however, a parent is not obligated to train the child to recite Shema, though it is advisable to teach one’s child the pasuk of “Shema Yisrael” as soon as he begins speaking.
Rashi (a”h) held that even when a child reaches the age of chinuch, it is unrealistic to expect a father to oversee his child to such an extent. In many instances, a father is not with the child at the time when Shema must be recited. Some fathers awaken early in the morning to pray before the child even wakes up and then they rush out to work. Due to practical difficulties, Rashi held that there is nor requirement for a father to train his son to recite Shema at the proper time.
The Shulchan Aruch follows Rashi’s view and does not require a father to train his son to recite Shema at the proper time each day and night. Nevertheless, when a parent has the opportunity, he should ensure that the child recites Shema at the proper time even though he is not required according to the halachah.