I used to miss it. But after being an adult more and more I have decided that being an adult is soooooooooooo much better than being a kid and now wouldn't go back to being a kid for all the money in the world.
Being a kid isn't really carefree without responsibilities and you have your life controlled.
Your parents or other caregivers say when you go to bed, what you wear, how long you can stay outside, when you have to go to the doctors etc.
You have lots of responsibilities as a kid.
Whenever I'm with my parents and my mom happens to see someone with a baby or toddler she mentions how she wish I was that little again and misses those days.
I told her before that I know she misses the days of me being a kid/baby/toddler, but I wouldn't relive those baby/toddler/kid days for anything in the world and I'm glad they're over to be honest.