Question

how to explain this that to kid with example

Answer 1

This is used to identify a specific person or thing close at hand or being indicated or experienced.
Example- This is my house.
Here "This" refers to the house which belongs to the person.

That is used to identify a specific person or thing observed or heard by the speaker.
Example- That boy is her brother.
Here the speaker stresses over the boy who is the girl's brother.

Answer 2

to kid-to tell sb sth that is not true ,especially as a joke
 ex-I thought he was kidding you when he said he was going out with a rockstar