My favourite cCar.

Proper nouns are always capitalized

Since my childhood, I've been fond of cars.

Since childhood, I've been fond of cars- 'I have been' expresses a continous action originating in the past using the verb 'to be'. verbs such as this show actions that happened in the past and continue to present time

My family says that I used to find the car advertisements in newspapers to see the cars.

Perfect. good job!

My favourite car brand in childhood was the Audi.

'when I was a child' or 'as a child' is more grammatically correct, was 'the' Audi. Putting a definite article highlights Audi it as a particular car brand.

I used to cut the Audi advertisement photos and keep them in my shelf.

Reflex verbs helps us to indicate that things or peple are being -re-refferred to within a given sentence.

Most of my toys include cars and bikes mostly.

Repetition of the same word. Add 's' to car to show plural form

When I used to go to school and come back home, I used towould sit at the window seat just to see the luxury cars.

"would' is a better form of the words "used to" and help to avoid repetition

Nowadays I am not that muchas interested in Audi brand that much because, now I know more about other brands or now I am aware of other brands.

Avoid word repetition and we use 'know about' if we do not have non-personal knowledge and "know' when we have full knowledge of something or someone

But I have still kept my hotwheels toy cars safely because ithey reminds me of my childhood.

We use a reflexive pronoun to indicate you are referring to the 'toys'.

To be honest, I still take a look at the current hHotw Wheels collection at shopping stores and malls.

Good job. Add a comma to express a thoughtful pause

I still find it very fascinating.

Excellent!

SEver since my childhood, I've been fond of cars.

My family says that I used to find thelook for car advertisements in newspapers to see the cars.

Look for / search = the act of trying to find something

My favourite car brand in my childhood was Audi.

Just for information, we often use the word "make" specifically for car manufacturers. An alternative for your sentence would be, "My favourite make of car during my childhood was Audi." We would use "model" for the specific car from that manufacturer. E.g., "the make and model of my car is a Volkswagen Polo."

I used to cut out the Audi advertisement photos and keep them in my shelf.

To physically remove it = cut out

Most of my toys included cars and bikes mostly.

No need to use the word "most" twice

When I used to go to school and come back home, I used to sit atin the window seat just(of the bus/car) just to be able to see the luxury cars.

Nowadays, I am not that much interested in Audi brand that much because, now I know morea lot of other brands.

No need to repeat "much" twice

But I have still kept my hHotw Wheels toy cars safely because ithey reminds me of my childhood.

Hot Wheels is a name, so is capitalized

To be honest, I still take a look at the current hHotw Wheels collections at shopping stores and malls.

I still find ithem very fascinating/interesting.

Just a comment, "fascinating" is VERY strong. If that's what you meant, great, but otherwise just "interesting" is more appropriate to say that you still enjoy looking at them.

Since my childhood, I've been fond of cars.

My favourite car brand in my childhood was Audi.

I used to cut out the Audi advertisement photos and keep ithem on my shelf.

Most of my toys includwere cars and bikes mostly.

When I used to go to school and come back home I used towould come back home from school, I would sit at the window seat just to see the luxury cars.

Nowadays I am not that muchas interested in the Audi brand that much because, now, as I know more other brands.