Young relative also thus taken in by good prank periodically (8)
I believe the answer is:
grandson
'young relative' is the definition.
'grandson' can be an answer for 'relative' (grandson is a type of relative). I'm not sure about the 'young' bit.
'also thus taken in by good prank periodically' is the wordplay.
'also' becomes 'and' (both can mean in addition).
'thus' becomes 'so' (synonyms).
'taken in by' is an insertion indicator.
'good' becomes 'g' (abbreviation).
'periodically' means one should take alternating letters (letters must be selected 'every so often').
The alternating letters of 'prank' are 'rn'.
'and'+'so'='andso'
'g'+'rn'='grn'
'andso' inserted inside 'grn' is 'GRANDSON'.
Can you help me to learn more?
(Other definitions for grandson that I've seen before include "issue for daughter, perhaps" , "Daughter's boy" , "Male descendent" , "Junior relative" , "Young male descendant" .)