Is it normal?.....................?

Is it normal to think about having kids and imagining what they would look like with every girlfriend i have? i know for women this is normal but for men, its usually not the first thing on our minds LOL. For some reason i really want to have kids and just expiernce my wife/girlfriend being pregnant and then having a little person running around.....but again....is this normal or can someone tell me why i might be having these fantasies all the sudden btw im 20 and well refined.