I love this clip so much - whilst there are no words, all the meaning is there, the emotion. You get such a strong sense of these little peoples' personalities. I love the way they use their voices.
I often get asked when did I start singing. I have struggled with this question, as I'm not rsure I ever didn't sing. For me, playing with vocal sounds is something I enjoy the feeling of. For example: "wooo!", singing a really high note, Shouty belting, lip trills, etc., etc - so many of these noises I've been making since I can remember.
Now I use all those very same sounds in a more formal singing, teaching or speaking context. I would consider all the noises I mentioned to be part of singing, or ways into singing. I'm not sure I've really nailed the answer to the question "What is Singing?," but how I use my voice, either for formally or informally, is something I've been honing since I was born (possibly before!)
Whilst growing up I thought I was just "messing about with sounds," like the conversation in this video. However, listening to how people speak, sing, make noice with their voices, making "silly" noises with my own voice, changing how I sing or speak, pretending to be my sister on the phone - all that has helped me no end in developing my own singing voice. And all of that enquiry into mine and everyone else's vocal capabilities is still enthralling.