Dog being rude towards my son
So for some time now, my wife and I have noticed a less than ideal attitude our dog has towards our son. When our son (3 years old) wants to go outside and play with our dog, Onyx generally tends to ignore him. He might play with him for a while but it seems Onyx is more interested in me. He waits by the door for me to come out and as I stand by the door and watch my son run out into the yard yelling in excitement, Onyx just stands in front of me wagging his tail and ignoring my son. I tell him to go play with him but he just turns around and expects me to go out and play. Once I close the door, Onyx might play with him for a few minutes but soon loses interest and sits by the door watching our son but apparently waiting for me.
Now I am the one who does most with Onyx. I take him and my son on long walks, I feed him, comb him, play with him, pet him, do tricks with him and give him more attention than anyone else in our house does. But we originally got him so our son will have a companion as they both grow up. So far, this is not quite the case. My son LOVES Onyx and is never rough or annoying towards him and never does anything that we see would make him like our son any less.
Now, I don't want to start being mean to Onyx or give him the cold shoulder so he will like me less and my son more, but I do want him to be more attached to my son. Any advice as to how I can accomplish this or what more can be done is very welcome. Thanks!!