I take everything show by show.
My youngest is almost four and LOVES Power Rangers. He is Autistic though...So this is more of a help to get him out of his shell. He gets really excited when it is on is more likely to get talkative with older brothers and it is pretty cool to watch when he likes the episode.
I HATE Cartoon Network. Yet it is the station that plays the older cartoons on Comcast out here....They love watching Looney Tunes and Flinstones....So sadly they end up seeing the nasty commercials for the later night shows they run...which tend to be disgusting.
Batman is another FAVORITE here.
Take them case by case. Most of the half hour shows are available On Demand or through most download services. You can take then one at a time on whether or not you think he should be watching them.
I would steer clear from most Cartoon Network programming...the mid morning and afternoons do not seem to be too bad...just do not leave the room while that channel is on because you never know when the grossness will start.