I am no counselor, but it seem to me that you are bored with each other. It may have a lot to do with your personalities. If you are both quiet, people pleasing types, or he is the blunt antisocial type, then you may just not have things in common and just continue to live thru the marriage because you are both committed to it.
Try understanding/reading/analyzing each other to see why you act the way you do (family history, fears, past hurts, etc) and work on communicating those things to each other.
You said your husband smiles with other people, so it would seem like other people have what you do not. Give him something to be excited about. Laugh more, play games and try to go out of the box at times so you can have fun with each other again.
The love might still be there, but you might just need to excite each other again. You said you don't feel anything for him anymore- which means you had it once...Love is not a feeling, it's a commitment. Feeling is a part of love but it's not all there is to it. Hope you both can find some common ground, at least for the kids sake. Best of luck.