Hmmm,i never know how to answer that question,we have 3 son's but it's not as simple as that,we lost one of our son's a few years back,after his death we both couldnt figure out what to say when we were asked how many kid's we have,if we said 2 we felt like we were forgetting about him, if we said 3 most people asked where the 3rd son was,then we had to explain what happened,explaining,talking & dwelling on his death nearly killed my wife & destroyed her teaching career.Now we say we have 3 children & if asked where the 3rd is we just say he's not living at home anymore.
Dont be so sure that you only want one child just yet,things change as time goes on,the older they get the more fun it is being a parent,we planned our 1st child & thought that would be it,then a few years later we decided on having another,then 18 months after the 2nd kid was born we jumped in with both feet & had the 3rd.