Women and servants are exempt from learning Torah, as it says "And you shall teach them to your sons to speak of them"- your sons and not your daughters. And (addressing the source of servants): all commandments that women are exempt from, servants are exempt from.
Children are not obligated in the commandment (of learning Torah), the father is obligated to teach him torah, as is explicit in the Torah (when it says) "and you will teach them to your sons".
This verse teaches (that one's father is obligated to teach) both young and older sons, which is why it specifically says "son"- (which is by nature) a young son- and not a man.
As our Sages said: 'When a child learns to speak, his father should teach him Torah and how to say Shema.' What is "Torah". In other words what can a child understand? -Rabbi Hamnuna says: (One should teach his child to say the verse) "Moshe commanded us to keep the Torah, the inheritance of Jacob"- only this verse, in order (to ensure) that one's son