1-Why is Mary veiled when she is depicted in her own house with just Joseph and Baby present?
  2-Is there any reason, why The Child Jesus is totally naked in many art works?

The nudity is to symbolise Truth and Purity, according to what I remember from Art History and a book called something in Latin.  BUT my professors were not at all Catholic.

Most of the early Christian art was loaded with sacred symbolism.  I have a book about the symbolism and I will try to remember to dig it up.  

BUT some of these paintings I am not so sure about!  I have to admit it makes me uncomfortable these days.   There is so much public filth and impurity it confuses the mind.