As nouns the difference between tomfoolery and hijinks
is that tomfoolery is foolish behaviour while hijinks is tricky and/or humorous behaviour.
tomfoolery
English
Noun
Foolish behaviour
(Cockney rhyming slang) jewellery.
hijinks
English
Alternative forms
* high jinks, hijinx
Noun
(hijinks)
Tricky and/or humorous behaviour.
Synonyms
* shenanigans