Loud child, oddly easy to understand (5)
I believe the answer is:
lucid
'easy to understand' is the definition.
(I've seen this before)
'loud child oddly' is the wordplay.
'oddly' means one should take alternating letters.
'loud'+'child'='loudchild'
The alternating letters of 'loudchild' are 'LUCID'.
(Other definitions for lucid that I've seen before include "Clearly expressed and altogether rational" , "Bright; sane" , "Shining, clearly" , "Clear-cut" , "Coherent" .)