Help with correct grammar

[Julia B]

My 4 year old son said a sentence the other day which I know if correct, but my husband believes is wrong. Please let me know which is correct and if possible why.
Did you see him doing that?
Did you see he doing that?
Thank you in advance for your response.

[MrPedantic]

Hello Julia

The first sentence is correct:

1. Did you see him doing that?

In this sentence, "him" is the object of the verb (i.e. the thing that is seen), and "doing that" is a participle phrase which gives more information about "him": you didn't just see "him", you saw what he was doing too.

The second sentence on the other hand is incorrect, as can be seen if we remove the participle phrase:

2. Did you see he?

Bye,

MrP