If I were telling this joke, I would word it like this:

This is a Chinese joke; can you understand it?

Father, who is watching TV: Son, would you get me a glass of water?
Son, who is 5 years old and playing with toys: Ok, dad.

A few minutes later...

Son: Dad, here is your water.
Father: Thank you, son.


The man's wife walks into the room...


Wife: Darling, did you let our son get you some water? 
Husband: Yes, and he did a great job, too. 
Wife: Well, you know he's just 5 years old and can't reach the sink, but he CAN reach the toilet.

This is a Chinese joke ,can you understand it?

Father : Hi, my dear son .can you help get me take a glass of water, please?(the father is watching TV)
Son : Ok,dad(the son is 5 years old and playing the his toys)

A few minutes later .

Son : Dad, give here is your water .
Father : My dear son ,thank you .


At this time,the mother is coming in.


Wife :Darling, did you let our son get you some water?
Husdand : yes ,he was did a good job.
Wife :He is just 5 years old .He cannot reach the water pool and I just saw him into leaving the toilet.

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That was a pretty funny one! :)