Your 3rd DSLR in 6 years and you don't do this for a living? That and the fact that you "never really took the time to learn how or to process" SUGGESTS to me that you are one of those people who just think that if they spend enough money or buy the right camera, good pictures will magically happen.
? They won't. Read that again. : ) Maybe I"m wrong, but I'm just throwin' a theory out there.
Having said that, you son is so stinkin' cute, you need to take lots of pictures of him and study them to learn how to make them better. this picture isn't tragic, it just isn't great. Choosing to take pics of him at night was setting yourself up for "technical difficulties" if you aren't technically competent. Low light presents the most difficult of conditions. You didn't do a bad job on that front, but it wasn't stellar either. Balancing flash and ambient is a skill you need to learn. In the meantime, take your important pics in the daylight, in open shade or in the shade with a bit of flash or a reflector.
As far as the expression goes, it looks like you caught him just before or just after a natural smile. Wide eyed innocent no smile is often better than a half way awkward expression. Timing is everything.
The prop/hat in the picture dominates unnecessarily. It comes between his adorable little face and the camera and screams for attention. Even if it were on his head (which might present its own technical challenges with shadow etc.), I might understand and appreciate that it was included. At least there would be a reason. But it seems to just be there because it was just there, and it detracts IMO.
Take the time to learn your camera functions first and shoot a lot of pics that you study afterwards. Ask for critique and learn from them, eventually you will be shooting masterpieces that your son will cherish when he has his own kids. He's a real cutie. Have fun!