Age is the most important thing you left out.
Up to age 2-2 1/2 kids do parallel play. Especially if he's been alone at home with only adults. He isn't familiar with kids and he might do parallel play for another 6 months or so. They don't really play with each other. They might both be playing cars but it's unorganized. They don't say "Hey, let's play races" or "I am driving this way, you drive that way". It's more like they're playing side by side but not with each other.
If he's older then maybe he's an introvert and is happy playing by himself. He's had 3-4 years of it. He will eventually learn to play with others. I'd assume that's why he's in child care if you don't work.
It's also normal for kids to decide to not eat and to eat only things they like.
Is he a picky eater at home? Well, let me rephrase that, are you a picky chef? Do you follow some food ideals that the child care center might not be like? If you only fix certain foods at home then this is new to him and it will take him some time to learn to try new things.
Does he eat when he gets home? Is he having BM's? Is he drinking other fluids? Is he dehydrated?
I wouldn't worry unless he was losing weight and that concerned the doc.
But until you mention his age and he's older than 3 1/2 I'm going to say he's being perfectly normal. Although I'm not surprised he's not eating cereal or pancakes or something like that when served at breakfast and he's not eating at least the fruit or eating a few bites of something at snacks or lunch.