Translation:Do you have a son?
"Do you have sons" should be correct because the question is 你有兒子嗎 without 你有一個兒子嗎
"Do you have a son" is "你有一个儿子吗?". The more correct translation of "你有儿子吗?" should be "Do you have sons?" DL should rather suggest "Do you have sons?".
If there is two sons that more than a son, they should be called sons, isn't it? I think "son" the word is countable.
Because "lad" is archaic in American english, and not a synonym of "son" although it technically means "boy"
'lad' is sometimes used to mean son, but not really generally, and in English most words in most contexts require articles, so a correct translation would be something like 'do you have a son?' or 'do you have any sons?'