When my niece was a little girl, she used to say really interesting things in all situations. We thought that we'd never forget them. She grew up and it turned out that we do not really remember much of what she said. Maybe less than 15 all family members combined.
When I had my own children, I made sure that nothing interesting they said would evaporate into nothingness. Whenever they said something funny or worth recording (the frequency is not that high), I used to slip away, quickly write it in my Evernote and come back. Later, I used to file everything into its proper place, one note full of stuff from each kid. Over time, that grew to hundreds of their sayings. We wouldn't have remembered more than 10 but now we know almost everything special they said. We will give those notes to them when they grow up.
This collection has been very precious to us. I just mention one random incident each forfrom my daughters and sonkids as examples.
Daughter 1 - 01/2015: One day I explained her how earth's tilt with different parts coming closer and farther form the sun causes summer and winter seasons. Later on one summer night, I took her to a grocery shop and when we reached the freezer section for an ice cream, she gently said to me: Papa"Papa, earth has gone farther away from the sun."
Daughter 2 - No record of date: One day she was grumpy about something. I asked her, "Do you want to put it behind you?" She saidreplied, "No, then it will follow me!"
Son - 03/2017: My son was 3 when he asked me this question: Air"Air has no colors, why Papa, why?" (Most kids would say air is invisible, and I liked his imaginative way of phrasing this question).
All kids in the world have their unique perspectives and say things that have never been said in the world before. If you have some in family, I highly recommend this kind of recording that would nicely complement the photos and videos other kids would have.
It seems old fashioned but even now when I stumble upon any of this while organizing my Evernote, I feel overwhelmed with joy and love. They would appreciate it too in the later parts of their lives.