Compare and Contrast

I am so unevenly distributed in Language Development class. It's an online class, and I'm not good at keeping up with those, but an aspiring SLP's gotta do what an aspiring SLP's gotta do. I'm behind in the reading and the lectures, but I already got my language sample for the project that isn't due until November 13. Go figure.
I will call the 2 1/2 year old whose language I sampled J. I know, me and J names! He seemed to be right where he was supposed to be linguistically and cognitively. I had a tape recorder, but I was writing things down as well. I was amazed that when I took my attention off of him to write something down, I didn't lose him. He was perfectly willing to engage with me when I was done writing. The last time I did something like this was with Joey in his scattered phase, and if I took my attention off of him to write something down he was off on the other side of the room talking to himself like there was no tomorrow, bless him.
His sister (whose is maybe in 1st grade) was out there too, and was able to provide some translation services. I've noticed before that older siblings understand their younger siblings' early speech better than their parents do. I wonder if anyone has done research on that? At one point I was talking to J's mother while J and his sister played on the swingset. The sister, trying to be helpful (and I suspect get some attention ;) ), kept hollering across the yard, "J said 'swing'! J said, 'leaf'!" I made sure to say, "Thank you! I'll be sure to write that down!" and actually write it down, even though I hadn't heard it myself and I don't know if I could actually count it.
His well-meaning mother kept telling J to "talk to Miss. Katie" and bringing out books for him to look at, but I got the longer utterances from him when he was riding around on his bike. Child-directed play is a hard concept to grasp and I didn't quite know how to tell her that I was supposed to be getting as natural a sample as possible. She was so enthusiastic and seemed to want to show off her son's language abilities, so I let her. I assured her that he seemed right on track and even a little ahead to me. If I do much more of this, I need to find a better way to prep my parents.