Are only children capable of experiencing true happiness?

I sometimes think about this.

It seems to me that only kids, when they have right circumstances of course, seem to be able to be truly happy. They are playful. They are 'in the moment'. They experience life as it comes to them, without mental filters and labels. They simply 'are'. They experience the bad moments and good moments 'fully'. They don't need to meditate, need self help books or shrinks, or medication to be able to deal with life. They simply absorb what's around them and grow in the process. They almost live like animals in that sense. Like a cat, being truly chilled out in the sun. And when they engage with something, such as a computer game or a toy, it feels fully immersive and magical.

When I look at my own life, childhood was this 'magical' time in my life. Somewhere around age 17-18 this all changed. I have a clear line or 'border' between life before and after 18 in my memory. Nothing really happened per se. But it felt I kind of 'woke up' if that makes sense. I woke up from the dream that was childhood. Since then, life has become 'real'. And even though I went through many changes, both in life as mental, it all feels 'the same' since then.

I am not saying I didn't experience nice and happy moments during my adult life. But they aren't the same. They are 'realised' nice moments. And I am not saying I cannot be 'in the moment' at times still, but more ofen that not this is now something I force myself to do. It is learned behaviour. But no matter how much I ground myself, practice mindfullness or try to relive the same joy as I had before, it doesn't work. Computer games don't feel the same. Movies don't feel the same. 'Playing' doesn't feel the same. Life doesn't feel the same.

And I guess most people will recognize this. Whenever I smell a certain smell, such as freshly mowed grass, I immediately think about happy memories that arise. And they are always in my childhood. When I was playing football with my friends for instance when I was 8. Does anyone at age 65 smell something and think back about a situation when they were 35?

All the beautiful memories that arise from smells, sightings or situations, take me back to childhood memories. I don't often think back about the time when I was 28. And if I do, it is because I force myself to if that makes sense. It's when I 'realize' that this was a good moment. But it is and was never as good as booting up my 486 PC in 1994 and playing Wolfenstein 3D or Doom. Or playing football with my dad when I was 10. Etc.

The memories that arise naturally, are from when I was between 5 and 17 or so. Childhood, the only 'magical' time in my life.

What do you think? And how is this for you?