Suddenly appear when Dad gets out of bed (3,2)
I believe the answer is:
pop up
'suddenly appear' is the definition.
(I've seen this before)
'dad gets out of bed' is the wordplay.
'dad' becomes 'pop' (synonyms).
'gets' means one lot of letters go next to another.
'out of bed' becomes 'up' (synonyms).
'pop'+'up'='POP-UP'
'when' acts as a link.
(Other definitions for pop up that I've seen before include "book for youngster" , "three-dimensional picture book" , "Appear (like toast?)" , "Appear suddenly or unexpectedly" , "which may interrupt computer user" .)