I too sponsor a child. Received a call from them today with no answer after I picked up. It took me a bit to answer so I may have simply missed them right as I answered.
I called the number back and it belongs to World Vision. I sponsor a child through them, so they were either calling me about a problem with something or to raise money for the earthquake in Nepal.
I also received a call from this number but did not answer it. They did not leave a message. However, after reading Jennifer's comment above, I too sponsor a child through World Vision - but my call was received today.