Scheme involves close to twenty exercises in which small children can lark about (7)
I believe the answer is:
playpen
'in which small children can lark about' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'scheme involves close to twenty exercises' is the wordplay.
'scheme' becomes 'plan' (I've seen this before).
'involves' is an insertion indicator.
'close to' says to take the final letters (the close/ending of).
'exercises' becomes 'pe'.
The final letter of 'twenty' is 'y'.
'y'+'pe'='ype'
'plan' placed around 'ype' is 'PLAYPEN'.
Can you help me to learn more?
(Other definitions for playpen that I've seen before include "device to capture the young" , "Limited room for amusement" , "Nipper stuck here" , "Child's enclosure" , "Enclosure for kids" .)