OP, I think you are having a hard time on here but I just want to point out that you are a wicked stepmother and therefore whatever you will be wrong.
Thank you letter activity with your child only - wrong because you are leaving out the SC
Thank you letter activity with all the kids - wrong because you ar massively overstepping an activity their parents should be doing and you are not their mother.
Also, I get the impression that a lot of posters don’t send thank you cards ordinarily.
A thank you card is for something specific.
Dear Jane, thank you for the ugly sweater. It is perfect for me to wear to next year’s competition and I will get first place. It was so kind of you to think of me. Love Niece
Older children can easily write that themselves, albeit with some prompting. With younger children, parents write and children sign or draw.
I would never expect a letter to say:
Dear Jane, thank you for the ugly sweater for Niece, the train set for Nephew and the bag for Another. We all love them and will play or use them daily. Love from niece, nephew and another.
If Jane gave three people three different things, then Jane gets three thank you letters.and the works won’t end it they are written and posted at different times!
Just a suspicion, I think the issue is that you have made your DH look bad because it hadn’t occurred to him to do thank you cards with the kids and you are now out parenting him in front of his relatives.
On another point, I was the youngest of three children. We all sat down at separate times with my mother to do our thank you letters. Different children needed different levels of support. When I started drawing pictures to be included in a thank you, the eldest was early teens and had lots of experience doing thank yous. He needed a quiet place for half an hour and mum’s address book and a supply of stamps. Middle child hated writing and needed closer supervision and encouragement. I mostly needed to be told to sit still and give my thoughts on the present so mum could write the words for me while I drew a picture or wrote my name until was old enough to do more by myself.
I think the people complaining dint really send or receive thank you notes themselves. They don’t really understand what goes into it or what the recipient gets from it. Their loss.