"shall be seen (all your males"): Yochanan b. Dehavai says in the name of R. Yehudah: One who is blind in one eye is exempt from "being seen," it being written "yeraeh" ("shall be seen," which can also be read as) "yireh" ("shall see"). Just as he comes to see (with both of his eyes), so shall be come to be seen.
"males": to exclude females. "your males": to exclude a tumtum (one whose sex is in doubt) and a hermaphrodite.
Which minor is exempt? One who cannot "ride" on his father's shoulder and go up to Jerusalem to the Temple mount. These are the words of Beth Shammai, it being written "your males." Beth Hillel say: One who cannot hold on to his father's hand and go up to Jerusalem to the Temple mount, it being written (Shemoth 23:14) "Three regalim (festivals)," lit., "feet."