Teaching the kids about Charity

Most every Christmas, we set aside some money to do some sort of charity at Christmas. I had almost forgotten about it this year with everything going on, but Laura asked if I wanted to help her take some toys to an orphanage. It was very last minute, so at church we let the Relief Society know what we were doing and asked if anyone wanted to donate or go with us to deliver. Some donated and two others wanted to go with us. So this afternoon, one of the other women, Norah, and I took my kids to some stalls by the lake and the tianguis to look for some inexpensive toys. My kids were the best help in the "what would you want?" department, because they insisted they needed about half the toys themselves. I continually had to remind them that the toys and other things were not for us, but for some kids without any parents. I think they may have considered that a fair trade; parents for toys. After about 3 hours and 2500 pesos were spent, we felt like we were ready to go.
I was pretty excited. I have never been to an orphanage before and had no idea what to expect. This one has about 70 kids between the ages of 6 months and 16 years old.
When we arrived the kids gathered around and seemed very excited by the 2 pinatas we brought for Christmas Eve. We handed each of the kids a toy and I was pretty impressed with how polite and grateful they were. There was very little complaining about what they got, or even trading. We didn't spend very long there, but I hope my kids were impressed by how small and crowded it was. We asked them what they thought and Riley said it was kind of stinky. Amelia said she would not want to live there with all those kids and Jane said nothing.
How do you teach kids to be grateful for what they have and want to help others that aren't as fortunate? I just don't know. This was our stab in the dark.