Mishnah Niddah 5:4: A girl three years and one day old can become sanctified [for marriage, i.e. engaged] through intercourse; and if she had relations with a yavam [one obligated to perform leverite marriage], he has acquired her [as his wife]; and one is liable for [having relations with] a married woman on her account [if she is married]; and she renders one who sleeps with her impure [if she is a niddah] such that he renders impure that which he sits upon, the lower [layer of bedding, even if he does not touch it directly], just like the upper [layer of bedding]. If she marries a priest, she can eat terumah. If someone invalid [for the priesthood] had relations with her, she becomes invalid for the priesthood. If any one of the illicit relatives stated in the Torah had relations with her, they are put to death on her account, but she is exempt. If she is younger than that, it is like putting a finger in an eye.

בַּת שָׁלשׁ שָׁנִים וְיוֹם אֶחָד, מִתְקַדֶּשֶׁת בְּבִיאָה. וְאִם בָּא עָלֶיהָ יָבָם, קְנָאָהּ. וְחַיָּבִין עָלֶיהָ מִשּׁוּם אֵשֶׁת אִישׁ, וּמְטַמְּאָה אֶת בּוֹעֲלָהּ לְטַמֵּא מִשְׁכָּב תַּחְתּוֹן כָּעֶלְיוֹן. נִשֵּׂאת לְכֹהֵן, תֹּאכַל בַּתְּרוּמָה. בָּא עָלֶיהָ אַחַד מִן הַפְּסוּלִים, פְּסָלָהּ מִן הַכְּהֻנָּה. בָּא עָלֶיהָ אַחַד מִכָּל הָעֲרָיוֹת הָאֲמוּרוֹת בַּתּוֹרָה, מוּמָתִין עַל יָדָהּ, וְהִיא פְטוּרָה. פָּחוֹת מִכָּן, כְּנוֹתֵן אֶצְבַּע בָּעָיִן:

Mishnah Niddah 5:5: If a boy of nine years and one day has relations with his yevamah [a widow of his childless brother], he acquires her [as his wife]. And he does not [need to] give her a bill of divorce until he grows up. And he can be rendered impure by a niddah, such that he renders impure that which hes sits upon, the lower [layer, even if he does not touch it directly], just as the upper [layer]; and he can render one [with whom he had relations] invalid [from being able eat terumah]; and he cannot feed one terumah [i.e. cause someone to be permitted to eat it on his account]; and he can render an animal invalid from [being able to be sacrificed] upon the alter [i.e. if he had relations with it, that is sufficient to render it invalid as a sacrifice], and it is stoned on his account. And if he had relations with any of the illicit relatives stated in the Torah, they are killed on his account, and he is exempt.

בֶּן תֵּשַׁע שָׁנִים וְיוֹם אֶחָד שֶׁבָּא עַל יְבִמְתּוֹ, קְנָאָהּ. וְאֵינוֹ נוֹתֵן גֵּט עַד שֶׁיַּגְדִּיל. וּמִטַּמֵּא בְנִדָּה, לְטַמֵּא מִשְׁכָּב תַּחְתּוֹן כָּעֶלְיוֹן. וּפוֹסֵל וְאֵינוֹ מַאֲכִיל בַּתְּרוּמָה. וּפוֹסֵל אֶת הַבְּהֵמָה מֵעַל גַּבֵּי הַמִּזְבֵּחַ, וְנִסְקֶלֶת עַל יָדוֹ. וְאִם בָּא עַל אַחַת מִכָּל הָעֲרָיוֹת הָאֲמוּרוֹת בַּתּוֹרָה, מוּמָתִים עַל יָדוֹ, וְהוּא פָטוּר: