I'd rather sponsor a Nepalese child through education tbh. There are many charities that do with a non-religious agenda.
I'd rather do that, than send a shoebox / sponsorship with a Christian message. Even if that child IS Christian. Many Christians also feel its inappropriate to do so, in some areas of the world.
When a charity makes the point that they are Christian they have a particular agenda which is in addition to the work that they do. This can be ethical, but the point is that it immediately carries a cultural sensitivity that should be respected. There is nothing wrong with Christian charity. Its a good thing. But it also has a point to why it is a Christian charity rather than a neutral charity without a religious background.
The issue with having Christian messages at all, in a box raises a conflict of interest question about what the purpose of their charity work is about. Is it to help or to encourage particular religious beliefs? Being able to answer the question to the satisfaction of those with criticisms is crucial. Either so they can support it in the future, or can continue to level criticism.
People should be free to voice ANY concern, without fear. The problem is that this particular charity had a problem with this in the UK, where people are more able to raise concerns and challenge practices. There are places in the world where this is much more difficult. That again raises questions.
The lack of transparency, the information that the charity gives themselves and the aggressive way in which they approach criticism creates a dynamic which is unhealthy and many people are very suspicious about and dislike.
People should be able to know exactly what their donations are for, and what a charity's full intentions are and whether they match with their own beliefs.
May I ask, do you have links yourself to this charity? I know that they have had regular posters who have been quite heavily involved with the charity on MN in the past.