When you were a child, what did you want to be in the future? When you were a child, what did you want to be in the future?

Space after comma

When I was a child, I wanted to be an astronaut. When I was a child, I wanted to be an astronaut.

When I was a child, I wanted to be an astronaut. When I was a child, I wanted to be an astronaut.

Comma after "When [subject] [verb] [additional information]"

I've liked the space and often read a picture books of the space. I liked space and often read picture books of space.

"Space" doesn't need "the" when you use it to mean "宇宙."

I've liked the loved hearing about outer space and often read a picture book of theabout space. I loved hearing about outer space and often read a picture book about space.

I've liked the space and often read a picture book of theabout space. I liked space and often read a picture book about space.

If you read one book multiple times your sentence is correct If you read multiple books about space, it would be "picture books" instead of "a picture book"

I've liked the space and often read a picture book of the space. I've liked space and often read a picture book of space.

Since I found it's very hard to become an astronaut, I realized my dream was just a dream. Since I found it's very hard to become an astronaut, I realized my dream was just a dream.

Since I found out it's very hard to be an astronaut, I realized a dream was just a dream. Since I found out it's very hard to be an astronaut, I realized a dream was just a dream.

Since I found out that it's very hard to become an astronaut, I realized that my dream was a just dream. Since I found out that it's very hard to become an astronaut, I realized that my dream was a just dream.

"Found out that" means to discover, learn something for the first time "That" after "realize" because you add information that could be a standalone sentence

Since I found it's very hard to be an astronaut, I realized my dream was just dream. Since I found it's very hard to be an astronaut, I realized my dream was just dream.

But now, I have a dream to host my own art gallery one day, as I mentioned yesterday. But now I have another dream and that Iis to host my own art gallery one day, as I postmentioned yesterday. But now, I have a dream to host my own art gallery one day, as I mentioned yesterday. But now I have another dream and that is to host my own art gallery one day, as I mentioned yesterday.

But now, I have another dream that I will host my own art gallery one day, as I posted yesterday. But now, I have another dream that I will host my own art gallery one day, as I posted yesterday.

But now, I have another dream: that Io host my own art gallery one day, as I posted yesterday. But now, I have another dream: to host my own art gallery one day, as I posted yesterday.

Colon (:) to introduce something (in this case, your dream) Or you could write "I have another dream of hosting"

But now, I have another dream that Io host my own art gallery one day as I posted yesterday. But now, I have another dream to host my own art gallery one day as I posted yesterday.