Validity of Levirate Marriage of two Minors: Yevamot 111b
Validity of Levirate Marriage of a Male Minor and an Adult woman: Yevamot 111b [2x]; Kiddushin 19a
Whether there can be adultery if the levir is a minor: Kiddushin 19a
For a Female Minor
Validity of Levirate Marriage of a Female Minor: Yevamot 111b, 112b
The nature of the bond for a Brother-in-Law for Levirate Marriage with a Minor: Yevamot 110b-111a
Refusing one Brother-in-Law and then marrying the other: Yevamot 107b
If a Female Minor was married off by her father, & then was divorced and remarried, she doesn't do Levirate Marriage from that second marriage: Yevamot 109a