My son is also four and loves him some baseball. He's been to three Reds' games in the past year and I was amazed at how well he behaved and followed the game. He quickly picked up when to shout 'charge'! The last game we attended after watching Edwin make a play at third he shouts "you're my buddy Eddie!" But he spent most of his time looking for and shouting for Griffey (his favorite player). Now anytime the Reds are on he likes to watch it with his dad. He gets real excited if the Reds hit a home run(very excited if Griffey). I've created a monster.
Anytime we go outside he always wants to play baseball. He seldom uses the tee anymore and wants me to be "the pitcher". After watching so much baseball, he has his whole routine at the plate. He pounds the bat at the plate (trying very hard to break him of this), sometimes taps his shoes with the bat even though he's playing on grass and announces "Griffey Jr!". He's either Griffey or Dunn. He also likes Austin Kearns but trying to explain that he was traded took some time to sink in. (He now knows that Kearns plays on the Nationals.)
When he focuses on the ball, he makes pretty good contact -again when he focuses on the ball. We use the big plastic ball and oversized bat for now. He's still a little too wild with the bat and is not always aware of his surroundings. However when we have a catch it's with a soft baseball. He's still learning to catch so I have to very careful with him. He's got a strong arm that's a bit inconsistent. I showed him the other night how to properly throw the ball. He picked it up pretty quick.
Funny story: When we sometimes have a catch, he wants me to be the pitcher and he's the catcher (he even squats). Well after I threw a couple short of him (worried of him missing or me hitting him) he walks the ball to be and says "Pitcher! Throw it to my mit!" turns around and walks back to his spot.