Son asked dad why his nipples are diferent than mine and why his belly was diferent than mine?

So im 30 and my husband is 32 and we have a litle boy and he is 6 years old. We three were on the couch and my husband didnt have a shirt on (and thats a normal behavior of him ) and our son was in his lap face to his body because he was sleppy and our son started touching my husband nipples and for the first time... show more So im 30 and my husband is 32 and we have a litle boy and he is 6 years old.
We three were on the couch and my husband didnt have a shirt on (and thats a normal behavior of him ) and our son was in his lap face to his body because he was sleppy and our son started touching my husband nipples and for the first time he asked why my nipples were different than daddy´s. My husband "anwer" him saying "Mommy´s nipples are different beacause she needed to feed you when you were a baby and every time she feed you , mommys nipples got bigger" of course he was joking, but our son believe haha he have time to learn about the human body thats why my husband asnwer him like this i tought it was very funny haha.
He asked other thing that was " Why dad´s belly have strange shapes and mommys dont?" he was talking about his dad abs.
He one more time answer like "Well its because i go to the gym and men train there to have this strange shapes, kinda strange right son haha".
And he said to our son that his body its going to change in some years and that he wont have big nipples like mom but when he gets older he can have the "strange shapes" (Abs/muscles) like dad. And he said "Right now i dont want you to get older because i love you soo much and i need my litle boy".
Its normal at his age to ask this questions?
Should my husband asnwer him correctly next time he asked about something of the man/women body or still anwer him joking?
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