Answer:
   
   Some parents would say "yes" immediately; others would issue an
   outright refusal. The child knows her grandparents are not Jewish, and
   it might be helpful for her to see how they practice their religion
   and what sorts of things are important to them. But this must also be
   weighed against the potential for identity conflict and confusion in
   the child, who may begin to feel as though she is "sort-of" Christian,
   or Christian in some "honorary" kind of way. For young children (under
   10), it is probably not a good idea, as their Jewish identity is not
   yet fully-formed and they will definitely absorb the confusing message
   that Christianity is somehow just as much a part of them as their own
   religion.
   
   Note that this answer does not address some of the potential
   underlying reasons for the question; it assumes the child is being
   raised Jewish by both parents (one, quite likely, a convert, although
   there are situations where it is the grandparents that left Judaism
   after the children were born). The question gains significance if
   there is an attempt to raise the child with multiple faiths. Most of
   the main Jewish movements (Reform, Conservative, and of course
   Orthodoxy) do not believe that is possible, and recommend raising the
   child within Judaism only. However, the issue is quite complex, and
   some of the texts in the Intermarriage and Conversion reading list, in
   particular, the "After You've Done the Deed" section, are appropriate.
   URL: [5]http://www.scjfaq.org/rl/int-afterwards.html.