The Book "Einstein Never Used Flashcards"
Amazon.com: Einstein Never Used Flashcards: How Our Children Really Learn--and Why They Need to Play More and Memorize Less: Roberta Michnick Golinkoff, Kathy Hirsh-Pasek, Diane Eyer: Books
looks at the research about preschool. What it shows is that kids who go to academic preschools are more anxious and less creative than children who go to play based preschools. This book is very well written and easy to read--it's not horrible science writing.
The bottom line of the book is--talk to your kids, read to your kids, let your kids play and they will do better than if you encourage academics at this age.
We are fortunate that I can work minimal amounts and schedule what work I do around my husband's schedule. Last year we paid to hold a slot at one of the best play based preschools in our city. (We got the last slot for this coming school year.) We canceled our slot because we feel our son will do best at home with me where he can just play. We go to art and activity classes at the park and go to library story time. The rest of the time he just plays--by himself, with me, with friends.
I'd suggest to the OP to be more concerned about the fact that the TV is on at the place where he goes. That's probably a good way to turn your kid's brain to mush. Beyond that, if he's just playing, that's great. Play is kids' work.