Appear when old man's out of bed? (3,2)
I believe the answer is:
pop up
'appear' is the definition.
(popping up is a kind of appearing)
'old man's out of bed?' is the wordplay.
'old man' becomes 'pop' (both can mean one's father).
'out of bed?' becomes 'up' ('up' can be a synonym of 'out of bed').
'pop'+'up'='POP-UP'
'when' is the link.
(Other definitions for pop up that I've seen before include "which may interrupt computer user" , "Appear suddenly or unexpectedly" , "book for youngster" , "Appear (like toast?)" , "three-dimensional picture book" .)