Welcome to Gaia! ::

When I'm gone,
and the rain is pouring down,
just go outside,
and lie down on the ground.
Turn your beautiful face towards the clouds,
and remember me.
Every cool drop that hits your face,
imagine that I am kissing you there.
And when it falls on your palms,
I am holding your hands.
And when it falls on your arms
and your chest
and your waist,
I'm holding you tight.
And even when I'm gone for good,
Forever I live on
in your dreams,
and your memories,
and your heart and soul,
and forever in the rain.

I feel like this sounds more like song lyrics than a poem (which is by no means a bad thing!). To me, as song lyrics, it's perfect. As a poem, I personally feel that you should add a few words here and there like "*For* every coold drop that hits your face" but that's by no means something that needs to be changed, just a suggestion on what you could change. I really like the whole idea of this. If you ever plan on making it longer, you could do something with the dry body shape that would be left when the person stood up, since their body blocked the rain. Like this(That's art by Andy Goldsworthy btw)
But I don't thin there's anything that NEEDS to be changed. I too don't feel that that your writing is childish.