Be under the false impression, being immature, personally (3,7)

I believe the answer is:

kid oneself

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'be under the false impression' is the definition.
I know nothing about this answer so I can't judge whether this works.

'immature personally' is the wordplay.
'immature' becomes 'kid' (I can't justify this - if you can you should give a lot more credence to this answer).
'personally' becomes 'oneself' (I've seen this before).
'kid'+'oneself'='KID ONESELF'

'being' is the link.

Can you help me to learn more?

I've seen this clue in the Evening Standard.

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