Simple math word problem

When i was explaining the importance of water to my daughter, friends she had endless questions which i had to answer. Not only on science, she also asked me about math, English and almost all the subjects.

She wanted to know why is railway line said to be parallel lines. I had to explain her the details with a diagram. But she is too small to learn this but i appreciate her enthusiasm in learning new things.

She wanted to know learn how to add, i gave her some simple examples like...the apple example

You have two apples with you and i have two so count how many do we have in total.
She started counting with her tiny fingers 2+2=4

She shouted " Mom totally we have 4 apples".

Then i told her that this is the additional property of mathematics.

She wanted to learn more but then i stopped at this and asked her to have her dinner and go to sleep. Once she went to sleep, i started hunting for some math problems online which i can explain her as per age and i was preparing myself for the next session with my daughter.