The cool metal sank deep into his hands as he climbed the monkey bars. His legs swinged as he pushed himself towards the next bar. It was lonely here, in this Muggle playground. There were no kids, not even Muggle ones. He'd give anything to have a friend right now.
At the tender age of four, it's no wonder he forms the concept of imaginary friends in the space of ten minutes in a lonesome playground. He follows this shadowy figure over the equipment, watching how this kid, a year or so older then him, slides down the slide gracefully.
It makes everything easier, fun. The cool metal equipment the grounds of his imagination, and the means of tapping into it. He has no idea how these experiences will be the beginnings of him making friends at Hogwarts. He doesn't care anyway.