Question

I knew him since his childhod what is the wrong verb here

Answer 1

Knew is the wrong verb
the correct verb is know

Answer 2

Hey here is your answer

Here in the sentence 'I knew him since his childhood', the wrong verb used here is 'knew'

The correct sentence is 'I have been knowing him since his childhood' because in the sentence 'since' is used that means that I know him from the past and know him till the present