T.G.
I've had this same thing with most of my kids; it sounds like he has a fairly mild case that will probably resolve itself shortly.
I know it doesn't SEEM mild and that 'shortly' seems like an eternity, but what you're doing is perfect. With my girls, a casual approach worked best. We'd discuss what she wanted to do today, what her favorite part of the day would be, and when I'd come to pick her up. I tried not to minimize their feelings, but at the same time not play into the drama. Tough line to walk, but honestly more cuddling and carrying on really didn't help - it only made it worse! Being a little more matter-of-fact and, "OK, see you later honey!" cut short the drama and let us both get on with our lives.
There is little harder on us than the sobbing/crying thing at dropoff. Just remember that shortly after you've left, he's gotten on to the important business of playing! He's having a good time, honest!!