Guardian

[Lavender77]

"Child missing, having left room later perhaps" -M-E-/A---T

Also "It might be heard, perhaps endlessly, in valedictory cheers" I think it's rhetorical ---I-E
Thanks!

[dannyk13]

1.Amber alert

[scorpiojo]

Amber alert
Rhetorical device anag i(n) valedictor(y) cheer(s)

[Cryptomaniac]

Agree with both solutions. In the case of the first, it's (ch)AMBER + anagram of later, but still can't quite see where the definition part of the clue is - unless police issue an 'amber alert' when a child goes missing. Bit sneaky to mingle the definition with the solution mechanics.

[scorpiojo]

http://en.m.wikipedia.org/wiki/AMBER_Alert

[Mamyalynne]

//An AMBER Alert or a Child Abduction Emergency (SAME code: CAE) is a child abduction alert system. It originated in the United States in 1996.//