I just saw this the other day and it melted my heart. We had a similar experience with our youngest (Aries) teaching her big brother how to climb stairs (Sonic had previously just refused to go near our stairs until Aries started doing it). I wish I had gotten that on video too!!
I had to pull out my old video for you guys. When I watch it I feel like I wasn't paying any attention to Maddie like the second child who isn't getting any attention. http://youtu.be/EDUaqwTCB5w