A phase that is regularly used amongst kids is: 'I am going to tell on you.'
Taken from
http://www.focloir.ietell on
(v + prep) informal TRANSITIVE
inis ar
scéala a dhéanamh ar
sceith ar
he told on her rinne sé scéala uirthi
I am wondering what is the most natural or usual way to say 'I am going to tell on you' is. 'Inseoidh mé ort' sounds strange, but maybe it is fine.
Of course, the other side of this is that maybe the English phrase 'to tell on' came from the Irish? I never know what came first - the chicken or the egg......

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Is foghlaimeoir mé. I am a learner. DEFINITELY wait for others to confirm and/or improve.
Beatha teanga í a labhairt.