פירוש על יבמות 13:1

One who engages an orphaned minor, or a minor released from her father's domain, when she can perform miyun and all her laws will be explained in Siman 154. Rem"a: And see later on Siman 169 who is believed regarding a male and female minor if they [later] grew up. If it was doubtful if they were minors or not, it is a doubtful Kiddushin . Beit Din is able to stop from marrying the minor, just like her mother and her brothers have this right, and they are able to put conditions [on the marriage] that if she does miyun , she will lose all that is hers. But they don't have the right to marry off the minor ( Nimukei Yosef Perek Cherech ). And see later beginning of Siman 155.

A ketana [girl less than 12 years and a day old] who does not have a father, or she has a father but her father had married her off and she became a widow or she was divorced while still a ketana, and thus she becomes like an orphan in her father's lifetime for he has no authority over her anymore, and she is married off with her permission, since her marriage is only on a rabbinical level, if she does not like her husband, she does not need a get [bill of divorce] from him, but rather she can leave through [the law of] me'un [where she can simply denounce the marriage]. But if she was married off without her permission, or even if it was with her permission, but she didn't know to keep her marriage, she doesn't even need me'un. Rem"a: Ideally the court should make sure not to allow the marriage of an orphan ketana when it seems it will end in me'un. And we can only judge this according to what we can see (Hagahot Maimoni perek 11 in the name of R"Y).

What is [a case of] a ketana [a girl less than 12 and a day] who must do a me'un [i.e. refusal of marriage which allows her to leave her husband when she is married off as a ketana]? From 6 years old until 10 years old, we examine her according to her intellectual abilities, if she knows [that she must] guard her marriage, and that when she is married, that the guarding is not like the guarding of a nut or date or similar, that is [a case where] she needs to perform me'un. But if she does not know to guard her marriage, she needs not me'un, but rather she can leave to her mother's house, as if she were never married. Less than 6, even if her sense of understand is great, and she knows to guard, she does not need me'un. More than 10, even if she is very dumb, she needs me'un. Rem"a: Some say that all this is only when she is married off by the permission of her brother and mother, but if she was married off without their permission, she does not need me'un [to go free] (Hagahot Alfasi perek Bet Shammai). Some say that if she is already past toddler's age, she needs to do me'un (Bet Yosef in the name of the Ritva).