I feel I dreamed, but it'Most of the time, even though I know that I dreamed, the dream still feels vague.

I added “most of the time” since you’re talking about dreams in a general context. You could also say “usually” instead of “most of the time”.

I usually only catch the dream about its situationwhat situation the dream is about.

The other day, I had a dreamed, but I only called backcould only remember that it was about my childhood.

I think you might have wanted to say “recalled” here? If that is the case, you could replace “remember” with “recalled” in the sentence.

I think I could recall my dreams better when I was a kid.

Since it seems like you’re comparing yourself now with your younger self, I put “better”.

Unfortunately, most of the dreams I had were scary.

It’s not grammatically incorrect but it sounds more natural to include “I” to keep the consistency since you’re talking about your own dreams, not dreams in general.

Perhaps, I only remembered the scary dreams because I was a timid child.

The reason why you put “the” here is to show that you are referring to the scary dreams you had as a kid. Without the “the”, it sounds like you’re talking about it in a general context. Also, saying “I was timid” by itself doesn’t sound natural, since people usually use it as a phrase to describe what they were scared of, like “I was timid of ___”. Otherwise, you could also use “timid” as an adjective. Basically, my point is that using “timid” by itself sounds weird and kind of unnatural.