riddle - I am many things

_{This has been approved on sandbox}

I am a place of joy for the kids.

I make the job easier for adults with certain jobs.
I am a tree.

For the kids, I'm made of a lot of small pieces.
For the adults, I don't exist physically.
When I'm a tree, I can grow up to 60m and explode yearly.

That has been my life so far, but lately, I became a rule also.
What am I?

[Edit - after the question was answered: may contain spoilers]

This is part of my protest against sandboxing riddles. Same as this one

Answer

Are you :

The sandbox itself?

I am a place of joy for the kids.

Kids surely enjoy sandboxes.

I make the job easier for adults with certain jobs.

For developers of course!

I am a tree.

Well, indeed.

For the kids, I'm made of a lot of small pieces.

Sand comes in grains!

For the adults, I don't exist physically.

Sandboxes are not a real place for adults.

When I'm a tree, I can grow up to 60m and explode yearly.

Still refering to the sandbox tree.

That has been my life so far, but lately, I became a rule also.

The Riddle Sandbox!