To my amazement, she was at my classroom door asking for it in a very short time. When I handed it to her and she opened it, she looked furious. Thinking she was upset with me, I told her that I was sorry but that I thought she hadn't known that her son brought it to school and was sure she would want to know about it. She looked up and said "This card isn't addressed to me!!! and stormed off. Dumbfounded, I went back into the classroom. Sure enough, when my assistant and I checked the child's information sheet, his mother's name was different than the one the card was addressed to. I felt so bad about that and have no idea what the outcome was.
Note to parents.....be sure to screen items your child brings in for show and tell.