Post-apple-picking, we met up with some friends who have a tall two-year-old. Our guy is a short four-year-old. So, they looked roughly the same height. There's a lot of development difference between a four- and two-year-old. Speech complexity and toilet training come to mind.
But not a lot of it has much bearing on short-term hangouts! They pointed at planes and ponds, climbed onto things, did some jumps, and just ran together. I was mildly surprised by how compatible they were, but if you think about it, you do a lot of the same stuff outdoors with your friends for fairly extended periods as kids.