Question

Molibyście mi sprawdzić czy jest dobrze. jak coś źle to poprawki napiszcie.
(daje naj)
Hi Katrin!
I am writing to you because I want to tell you about a story which that happened to me.
Last weekend I went to the park for a walk with my boyfriend. It was very sunny, so we enjoyed the moments in the fresh air.
We were hearing crying children. Suddenly, we were runing on playground. We were seeing there little children. The girl was wearing in beautiful dress and the boy was wearing in suit. We approached them. It turned out that them lost their mother. Daniel took the girl on arms and we all went to a nearby police station. On-site tearful mother was waiting for her children. She thanked us.
We got back to the house. We was exhausted but delighted.
Now, I am waiting for on email from you.
See you soon.
Love,
Marika

Answer 1

I want to tell you a story that happened (about, which- zbędne)

We heard children who were crying. 

Then ,we ran to the playground.

There we saw little children.  T

he girl wore....the boy wore (Past Continues, moim zdaniem zbędny, Past Simple pasuje w tej sytuacji lepiej ) 

 It turned out that they lost....

Daniel took the girl in his arms and together we went ....

Inside,(zamiast tearful),we met the children's mother, tears were running on all her face.

We were (was tylko w 3 os. l.poj, zapamiętaj ! D) exhausted, but happy that we could help.

Now, I'm looking forward to hearing from you

Hm, nie było tak źle, aczkolwiek, trochę błędów było, mam nadzieję że nie ominąłem nic ważnego :)