Once upon a time, in a deeply magical forest there lived a princess named Leila.

"deep magical" sounds a little strange.

When she was born the whole kingdom gathered to see her beauty, she was as small as a ladybug and as beautiful as a picture, but none of her family knew that something very terrible willould happen to Leila when she faells asleep.

picture of what?

The tense appears to be past all the way through.

TWhen night came, her mother entered her room and kissed her for so long that she didn't notice it was alreadyit was past midnight owhen sher way out stood to leave.

This sentence is confusing because she doesn't leave until two sentences later.

The situation is also very creepy sounding at least in English.

All the guards, as well as her mothernd the King and father Queen, rushed into Leila's room, but Leila's bed was empty.

Whose mother? The subject of the sentence is kind of the bed the way it's written.

They searched and searched the whole castle and every part of her room but she was nowhere to be found.

HerLeila's mother cried so much that she didn't evenwithout even stoping to eat, drink or sleep for days.

Are we saying she literally cried for days and nights? For a fairy tale obviously this is okay but we want to be clear on what we're saying.

Hundreds andupon hundreds of guards went lookingsearched for her but she was nowhere to be found.

This is a small change that's not necessary but fits the style better

The King, her father, orde declared that whoever finds his daughter will getreceive one million golden coins.

This repetition (The King, her father) only makes sense if the audience is the youngest of the young. I think it might help to label your writing if it's going to be for very early children since the word choice and repetition become more important.

Days and dayyears passed and so had a year but Leila was nowhere to be found.

The Queen cried desperately: '' My dear, I miss our little beauty so much!

This sentence comes out of nowhere

The Queen replied: ''Meet knight Josip, he is going to help us find our little princess.''

He told her it was Josip.

It was athe princess!!!

When they came ''home''back, they sat down at the table and the knight told her everything.

She agreed andto stayed for a week.

That week was great for her.

I would recommend a stronger sentence if possible or leaving it out

After athat week, she said goodbye to the Queen and the King.

Or something like "After that week was over".

She finally wentreturned to the forest to be their greatest Queen of all times there.

The knight Josip gotreceived his money and his sister was cured.

you can use a little more specific vocab when you're writing longer form like this and it will come across a little better

The King and the Queen were happy to at least see their little girl from time to time.

They arranged on regular meetings in the forest orand in the castle.

Her mother cried so much that she didn't even eat, drink, or sleep for days.

This is a fairly advanced grammatical rule known as the oxford comma.

The King, her father, ordered that whoever finds his daughter willould get one million golden coins.

Days and days passed and so hadthen a year but Leila was nowhere to be found.

This is a weirdly phrased sentence. Something more natural would be:

Days and days passed but Leila was nowhere to be found, even a year later.

The Queen cried desperately: '' My dear, I miss our little beauty so much!

The king answered: '' Yes, but where do you plan to find him?"

The Queen replied: ''Meet knight Josip, he is going to help us find our little princess.''

This is correct, but for interest's sake the English equivalent of the name Josip is Joseph.

AccordListening to the Queen's desperate willplea, the King found Josip who was willing to help and the King asked him: ''Why do you want to help us?''

The sentence structure here doesn't make sense. In the sentence before, the queen had already found and introduced Josip. In this sentence, the King then starts to search for him. These contradict.

We don't have golden coins to buy her expensive medicine and when I heard about your reward, I knew I had to do it so you see that's why I want to do it."

If you bring my daughter alive to me, I will pay for your sister's medicine and I promise to give you two million golden coins."

A more natural way to say this would be:

If you find my daughter, I will pay for your sister's medicine and I promise to give you two million golden coins."

Josip replied: ''Thank you, my lord, w. When should I start?''.

A comma shouldn't be used in this case.

As soon as he came intoendered the forest, he felt a little scared but he remembered his sister and gathered thehis courage.

Half way inthrough the forest, he found the tree of golden apples but then he remembered that the King warned him that he would come across and see strange things in thate forest because it was magical.

When they camereturned ''home'', they sat down at the table and the knight told her everything.

Her state was one of a profoundShe was shocked but she trusted him.

Your sentence is technically correct, but it's not something that someone would say in English.

She was relaxed and then joined him on their way back to the kingdom.

The Queen cried: ''It's her, it's really her!''.

She finally wentwent back to the forest to be the greatest Queen of all times there.

They arranged on regular meetings in the forest or in the castle.