Yes, I know we're very late, but there's a reason (kind of).
I have an aunt and uncle with children only a few years older than mine,
Every year, until they turned 21, as is the custom in our family, I sent something for birthday and Christmas (a cheque as they got older). I never once got a thank you letter or call. Never even knew if they were received.
Which is odd because my Mum (uncle's sister) was a real stickler for thank you notes and I always made my boys send them.
Now my DC are almost adults. I know they haven't written and I've "mentioned" it a few times.
People were thanked in person for all other gifts, when they were received, with the exception of our neighbours who they have thanked in person since.
I'm not inclined to make them write to aunt and uncle but there's a part of me that's not comfortable with that. I'm also a bit disappointed that they need "making".
Would you insist?