Hi L.,
I have some thoughts on this
* You might take a look in your son's mouth see if he is cutting more teeth. If he is he might have an upset stomach or doesn't feel to good. It might be that the only reason he eats good in the morning is because his jaw, mouth and gums don't hurt but as the day progresses they start to.
* I would also talk to your daycare provider, see if he is eating the sameway there. If he isn't I would ask what she is getting him to eat.
* If he isn't eating dinner with you I would check and see what he is having at snack time, making sure he isn't to full when you get him home and when snack time is.
* I would also make sure he is getting a good nap during the daytime and he isn't overly tired when it's time to eat.
* The other thing it could be is that he is just a picky eater.
My 6 year old son was that way also. Now he eats everything.
Here are some ways to try and get him to eat though try ketchup, mustard, ranch, mayo etc. Also try different things like fruit cups, also buy deli meat and roll it up my daycare kids love this (they don't like it on bread, they also like mayo on their plate so they can dip the ham or turkey in it.)
If I put it on there flat they won't touch it but if I roll it up it's gone. Also if you have tried peanut butter and know he isn't allergic take a piece of bread and smash it down put a very thin layer on it, you could add jelly also if you like and then roll it up. Slice the bread in thin pinwheels, my kids loved this when they were little to.
My 6 year old dips his green beans, carrots and sausage in ketchup. He likes ketcup on his scrambled eggs, and mac n cheese. And loves carrots, cucumbers and salads with ranch. I hope this helps and by the way if he gets hungry enough he will eat. Also you can get the carnation instant breakfast and get the powder kind you can get the same flavors or the assorted. I was recommended that when I was pregnant with my son and when he was your sons age. It tastes pretty good and you could use as a snack it has all the vitamins and minerals in there. Goodluck W. mom of 4 and home child care provider.