Today Is Sunday

If children don't receive love from their parents, they will grow as people who are diffident of themselves, can't ensure their own value.

I have no children, no husband and am totally alone. My life is barren.

Well this is correct only if I understood the Japanese sentence correctly.

The context in which you're trying to use "barren" is also a bit unusual. Here's another example:

There have been droughts here for the last 6 months and the once rich earth is now barren.

If children can find no love from their parents, they will grow into people who are diffident of themselves, and cannot find self worth.

Haha I learnt a new word now. I never knew of "diffident" till now!

Children can be impressive if they've been brought up with ample love from their parents, and that adults shouldn't be oblivious of expressing their deep love toward them.

It's an unusual context to use "impressive". Here are more common uses:

For a 10-year-old to be able to write something so complicated; it sure is impressive!

I don't see why it is impressive that she wrote this proposal. After all, she has years of experience in this; it is expected that she should be able to do it.

The main motivation for children to aim at improving themselves more and more is the building of confidence based on numerous experiences that they felt be loved by their parents.

The meaning isn't wrong; it is indeed 中心的 but it when talking about motives we usually say "main motive" or the like.

Here are some examples:

The central theme in this book is love.
この本のメインテーマは「愛」です。

Central administration is key for the success of this plan.
この計画の成敗は集中管理によります。

I can describe myself as a very immature girl when I was a child who enjoyed imagining things, and I built my ability to be creative in novel-writing based on that.

It is easier to think of the usage of "premature" as "too early". If you think of it that way then it wouldn't fit the context of your current sentence. "Immature" is the word for your current sentence :).

Examples:

We have only run this program for just 1 week. It is premature to call it a success.

I was an excessively docile child towards my parents, at least superficially, until I went to high school.

We don't usually say "promoted" when we moved into higher levels of schooling.

I can't stop wondering of the secular world's tragic that is filled with numerous misery crimes.

Sentence doesn't look quite right. It is correct to say "secular world" though the rest of the meaning of the sentence is unclear and doesn't match up with the Japanese sentence.

Example:

The world is becoming more secular and interest in religion is dwindling.

To live without getting hurt from anyone is the certain vested right of every child in the world, and whenever adults find that this right has been infringed upon, they have to take action to deal with it.

It is too intricate for me to live on the life.

Usually "intricate" is used to describe material/physical items. When used for descriptions of non-material ideas, it will need to have a corresponding imagery (metaphor) for it to work. Sometimes it can also used to describe something that is complicated (because it is detailed). It can be both positive or negative.

Examples:

His web of intricate lies fell apart when his diary was discovered.

This design is very intricate. It must have been difficult to produce.

I can't stop obsessing over every tragedy I can anticipate.

She looks diffident but I love her all the more for that.

"All the more for it" / "All the more for that" / "All the more so" - It is almost a fixed phrase.