At my son's school the other day, I overhead a couple teachers in conversation about a student. One statement was that, often, the child was in charge of the dynamics at home. Then came the words I dreaded. " [The student] is an only child." In fact, this particular teacher has a few only children in her class. Apparently there are some similarities.
These are conversations that make me wary. I am an only child, and my husband and I are raising an only child. I know what a bad rap only children get. I have even known some of "those" sorts of only children - the ones who are self-absorbed, bossy, etc. I work really hard to make sure that (a) I don't act that way and (b) that my son doesn't act that way.
But it is hard to teach an only child not to be bossy. My son has an active imagination that drives 90% of his play. When he plays with others, they can't read his mind and therefore don't play the way he wants them to. I am proud of how he works at this, but it is something that will have to develop over time.
We also work very hard to have clear boundaries with him that we are the ones in charge. But, again, the dynamic of a three person family is just different than a five person family. We include him in decisions about where we want to go for the weekend or what we want to have for supper or what movie we want to watch. I have had to learn, as a parent, to tell him when he doesn't get a vote. We have to make a conscious choice to say it's "Daddy's turn to choose" or else he will think that he is an equal to the adults when it comes to making decisions.
Some people think it is easy to parent just one child. And it some ways it is. But, if the parents are aware of the pitfalls for only children, they have to work hard to parent in a way that diminishes those pitfalls!