My son is not quite 4 yet and has taken a real shine to baseball.

About 4-5 nights a week he asks me to go out with him and play baseball. Sometimes we play for 30 seconds, sometimes 45 or more minutes. I leave it up to him. Occasionally he'll rope Mom into catching or fielding so that our games have a bit of a faster pace. Once in awhile he'll drag Mom out there if I am unavailable.

We generally hit off the T for a few minutes, I soft toss a few balls to him, and he hits underhand pitching and and slow "shot put" type tosses. This week we are learning to take a small step before swinging the bat. To my suprise he made this transition pretty easily. We do all this with a wiffle ball and Fred Flintstone type bat.

We'll throw a tennis ball back and forth on the driveway so he can take grounders in the form of rollers or bouncers.

I have made small bases so he knows which direction to run them in, as well as learned about the infield and outfield.

We have a lot of fun when we play and only have a few basic rules:
1) We never throw our bat
2) when hitting we throw the ball back to the pitcher, we don't hit it with the bat
3) He pays a decent bit of attention to our game
4) He helps put the equipment away when we are done

Basic fundementals are:
1) Correct batting stance/setup
2) Bend at knees to field grounders
3) Target the receivers chest when throwing.

I have no idea where to progress with the boy from here. Is it appropriate to move on to little metal bats and tennis balls or would I be better served to start him off with baseball sized whiffle balls and bats? I think the metal bats would be too heavy for him to swing, but I haven't tied it yet.

Part of the joy he gets from our sessions is how far he can hit the ball, I'd be robbing him of some of that if we when to heavier equipment and mostly why I have been hesitant to introduce the heavier equipment.