As I always tell my son, "good manners are NEVER out of season" .... Truly, if someone has taken the time to give you a gift, a person can then sit down and write out a thank you note.... My husband's cousins for whom we always give money to on their birthdays and most recently, graduation NEVER send a thank you note... Oh wait, one time we got a text...
Many might think a thank you card is for the person who bought the gift, but I also believe it's important that the person who received it, show an attitude of gratitude in general......... in my house, the thank you card does show thanks to a person, but in the bigger picture of life, it also teaches my son to count his blessings and not to take the kindness of others for granted...
In my career, I've gotten two jobs because MY thank you notes stood above the rest....
Also, it's ok by me if the world is leaning towards not taking the time to send a thank you note... it makes MY son stand out because he always does....
keep teaching your child good manners.... it's a good thing in my opinion :)