I think it's okay to have the kid in there sometimes, but the clubhouse is the players "place." It's where they can shed whatever public persona or PR agenda they have and cuss, gossip, tell crude stories/jokes, pull pranks on others, vent, etc... probably some players felt that having a kid around "all the time" prevented that from happening.
The only analogy I can think of is if you have a group of buddies that you meet regularly or semi-regularly for beers, golf, bowling, whatever. What if one of those guys insisted on always bringing his kid along? Eventually, one of you guys would have to pull him aside and ask him not to bring the kid along all the time. In this case LaRoche decided he's not going to hang out with you guys for beers anymore.
It was his choice to make. And like 4mer said, they could have asked him to stop sucking as well.