My fFavourite tTime of the dDay My Favourite Time of the Day

While less important for informal writing, in formal writing we capitalize the first letter of important words in the title of a formal post or essay.

My fFavourite tTime of the dDay My Favourite Time of the Day

That's because my two kids fall asleepgo to bed at that time, so I can enjoy my spare time. That's because my two kids go to bed at that time, so I can enjoy my spare time.

Fall asleep isn't technically wrong, but going to bed might be a better fit. If this is their scheduled time to sleep, it's their "bedtime." Falling asleep is more for when they are actually asleep after going to bed.

That's because my two kids fall asleep at that time, and/so I can enjoy my spare time. That's because my two kids fall asleep at that time, and/so I can enjoy my spare time.

Or: “…at that time, and I have some free time.”

I usually learnstudy English or read a book until midnight. I usually study English or read a book until midnight.

Study is what you do in order to learn English. We would typically only use "learn" in the past tense in this context, as something you have already learned.

I usually learnstudy English, or read a book until midnight. I usually study English, or read a book until midnight.