Discontented older child's left wanting flowering plant (6)
I believe the answer is:
orchid
'flowering plant' is the definition.
(orchid is a kind of flowering plant)
'discontented older child's left wanting' is the wordplay.
'discontented' says to hollow out the word (remove centre letters) (the word's contents are removed).
'child' becomes 'ch' (abbreviation for child).
'left wanting' becomes 'id' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'older' with its middle taken out is 'or'.
'or'+'ch'+'id'='ORCHID'
Can you help me to learn more?
(Other definitions for orchid that I've seen before include "Much sought-after family of plants" , "Lush and expensive tropical flower" , "Plant with complex blooms" , "Exotic and much treasured flower" , "lady's slipper, perhaps" .)