My son looks down whenever he sees other kids his age

Ki

My 15 month old doesn’t know how to engage with other children because we’ve kept him away from everyone for pretty much his whole life. But now, we’re starting to take him to the park to meet and see other children. But whenever he interacts with someone his own age, he just stares intently down. And then walks away. Is there a way to encourage him to play? Or should I just let him be? I’m guessing it’s just his age where he doesn’t really interact with other kids yet.