All are obligated in re'iyah except for a deaf person, an imbecile, a minor, a person of undetermined sex, a hermaphrodite, women, slaves who have not been freed, the lame, the blind, the infirm, the aged, and one who is unable to ascend by foot.  Who is deemed a minor? Whoever cannot ride on his father's shoulders and ascend from Jerusalem to the Temple Mount —- [these are] the words of Beis Shammai.  Beis Hillel say: Whoever cannot hold his father's hand and ascend from Jerusalem to the Temple Mount, for the verse states: three pilgrimages (Exodus 23:14).