The Grand Ayatollah Makarem Shirazi answered a question about the guardianship of disbelieving (Kafir) child by Muslims.
Question: Can the Muslim man and woman be guardians for a disbelieving child who is Najes (impure)?
The Grand Ayatollah Makarem: If the guardianship and education of the child are given to them, in Taharat (cleanliness) that child follows them.
source : Shafaqna