TV programme, extremely childish — so what's new? (4,4)
I believe the answer is:
chat show
'tv programme' is the definition.
(I've seen this before)
'extremely childish so what's new?' is the wordplay.
'extremely' suggests removing the centre (only the extremes of the word are used).
'new?' is an anagram indicator (I've seen 'new' mean this).
'childish' with its centre taken out is 'ch'.
'so'+'what'='sowhat'
'sowhat' anagrammed gives 'atshow'.
'ch'+'atshow'='CHAT SHOW'
(Other definitions for chat show that I've seen before include "Airing of gas" , "TV programme in which celebrities are interviewed informally" , "TV celeb programme" , "Programme on which celebs talk" , "TV or radio interview programme" .)