Going to a farm can be a little scary for a young person. They have much less experience than an adult regarding which animals bite and which don't, and therefore which animals are safe to pet. This little guy looks like he'd try to win over some cows by wearing a t-shirt with a cow's face on it, showing that he's on their side. It's an adorable idea, and it actually looks like it might have worked!
Look how startled that cow looks. It's almost as if it's seen the face on the t-shirt, and recognized it. Perhaps it thinks it's a picture of a close friend or relative. Either way, it's brought the cow and the boy a little closer together, and that can only be a good thing. This is a nice, wholesome image. We wonder if he wore different shirts for the horses and the pigs later on?