There's no law against having more or less than two given names, but as parents of a child born in North America, chances are decidedly in favor of your choosing two for the following reasons:
It's commonly accepted. Do you know anyone without a middle name, or, for that matter, with more than one? And if you do, have you ever wondered why? It's like having two eyes, two ears, and one nose. We expect it.
It fits on most legal forms. Almost every form these days provides a place to write your first and last name, as well as a spot to denote your middle name, or, at least, its beginning letter. This, by the way, is also a good reason for limiting your selection to just one middle name, as most forms don't allow for anything more than this. If your child has four names (two of them being middle names), there's a good chance that he or she will often be limited to using only one of them.
It prevents your child from receiving the middle name Nmi. This doesn't happen as much anymore, but about 20 years ago, many computer programs were coded to recognize three names and only three names. If a middle name wasn't indicated, the program would insert NMI, which is military shorthand for “no middle initial.” While most folks do know what this acronym means, there are still some who don't, and if it shows up on a list of any sort, they think it's some exotic middle name. This may seem too silly to be true, but I've seen it and I've heard it more than once.
It gives your child more flexibility when it comes to deciding the name he or she wants to be called by. It's not uncommon for people to use their middle name at some point in their lives—you might even be one of them. Why? Sometimes they don't like their first name or are just plain tired of it. Or they may be asked to use their middle name to differentiate themselves from others who have the same first name (just like centuries ago!), such as in classrooms where popular naming styles have resulted in a few too many Courtneys or Michaels or Emilys.
Not giving your child a middle name can set him or her apart from the rest of the kids, just like an unusual or an uncommon name can.
What's in a Name
Many aspiring actors become stars when they trade their first names for middle names. Here's just a few: Warren Beatty (Henry Warren Beaty); Dyan Cannon (Samille Diane Friesen); Diahann Carroll (Carol Diahann Johnson); Faye Dunaway (Dorothy Faye Dunaway); Lauren Hutton (Mary Laurence Hutton); Gregory Peck (Eldred Gregory Peck); Robert Redford (Charles Robert Redford Jr.).
This last point may seem pretty far-fetched, but remember: if there's a reason, regardless how slight, for kids to ridicule each other in any way, they'll usually do it. It seems kind of funny that kids without middle names can become the target for as much ridicule as the ones with unusual or strange names, but it does happen. So, since you're the type of parents who want to shield their little ones from as much uncalled-for abuse as possible, you're going to choose a middle name, right? Let's make it a good one!