Observations

You know your 4 year old is learning new words and phrases when he says:
Mama, I have ‘decided’ to become Batman for Halloween. No, ‘actually’, I will be Spider man and then Batman.
or
"Ooh, that was close!"

You know he is a TV bug when he says:
Mama, my show is on at 8/7 central

You know he loves his sister when:
When he kisses her and hugs her until she gets agitated.
Asks her, "A, you are OK? Ha?" when she falls or cry
When he gets her water from the refrigerator and helps her to drink a few sips before he does
When, at the toy store, he was more concerned about what he was going to get her instead of himself