I know when I tried to play with kids at school (a hearing school) there was almost non-stop communication between the other kids: about rules, correcting a kid doing something "wrong", asking another kid if so-and-so wanted to play, about what they watched or did last night, etc etc. That's how the "hearing play" that I experienced was different from my "home play". When I mentioned that I studied developmental psychology, anyone who has read my previous posts would know I majored in psychology in college. In college, I learned the importance of play not only with human children, but also with animals learning the skills they need to survive and thrive as adults. If your question (which left me a little confused) was refering to how can someone study developmental psychology as a child when playing with their siblings, I wasn't saying that. I was a smart kid, but not a child prodigy. If your question was refering to how can developmental psychology learn anything from sibling play, the same as anything else: observation. If your question is refering to the importance of play, play mimics what children see adults doing. For example, playing house a child can mimic and learn social skills. A child playing with a doll can learn empathy. etc etc. Hope that answer your question.