It was happend when my son might be 3 or 4 years old.>>It happened when my son was about 3 or 4 years old.
My son liked rain boots.
>>My son liked wearing rain boots.
OR
>>My son liked his rain boots.
So, he usually wore his rainboots without thinking the weather.
>>So, he usually wore his rain boots without thinking about the weather.
It was after rainny day.
>>It was after a rainy day.
There were a lot of puddles on the road.
>>CORRECT
My son was stomping on it.
>>My son was stomping in it.
He might walked all puddles on that place.
>>He walked through all the puddles in that place.
I was worried his laundry but I couldn't tell him anything like warning that "not to step in the puddle".
>>I was worried about his clothes, but I couldn't tell him anything, like warning him not to step in the puddle.
Because I could kow that he was extremly excited and I was happy to see his smile.
>>Because I knew that he was extremely excited, and I was happy to see his smile.
Also it could be my memory with son.
>>Also, it could be a memory with my son.
As you know he doesn't remember the story.
>>As you know, he doesn't remember the story.
It remains only on my recording on my phone and brain.
>>It remains only on my phone's recording and in my memory.