Why do I feel so depressed when I think about the wonderful days of my childhood and compare them to now? :(?

I really miss being a kid when my parents were a little younger, school was simple, and when I got to play games and hang out with my family all day. I still do those things but because of school work and the business of everyone's life (along with the growing complexity of the world), those days are impossible to relieve and only remain as memories. What can I do?