They loved each other.
They played with each other very much.
The cloud played the fool and seed also danced for cloud.
Sometimes they wrote to each other and wind delivered their letters.
Because they where far from each other.
One day, they decided to play hide-and-seek.
The seed closed its eyes and cloud hid.
The seed found it behind the sun.
Then cloud should close its eyes.
Seed hid under ground and cloud couldn't find it.
The cloud thought that it never would [would never] see seed again, so cried hard.
Because of its tears the seed grew up and climbed the sky.
Climb, particularly in view of its meaning in your story, is an intransitive verb. To be used correctly there in your sentence, it requires a preposition: climbed up. Of course, it should be noted that ascend describes a better skyward movement.
Cloud was glad when it saw a bridge between sky and ground.
It's better to use a change-of-state verb here; something like become; or other structures:
- He rejoiced at seeing ....,
- Seeing the bridge delighted him.
A bridge connecting the sky to the ground (= the ground to the sky).
And came down to find its friend.
When [he or she] reached there, while seed was changed made a joke with cloud.
Apparently, there's an ongoing action at work; you could say: while the seed was changing. Change can be used as an intransitive verb. Otherwise, was being changed should be used, which doesn’t sound to be perfectly natural.
Was the seed undergoing a metamorphosis? By change, do you mean going up or growing up?
Cloud knew [recognized is better here] seed and embraced it.
The cloud
Afterwards many clouds for finding their seeds travel to the ground and then fog happens!
Many clouds, trying to find their seeds, descend over/ upon the ground, and that's why fog is formed.
Hang and fall can also be used with fog.
Fall is associated with a gloomy mood. Cloud itself can be used as a verb too.
So your explanation of this meteorological phenomenon involves a process of
matchmaking between the friend-seeking clouds and waiting seeds. Connotatively, it's believable.