i don’t think it’s your parents’ job to buy a bauble.
I have a 14 yo myself. And obviously she was 11 before that. In itself, I don’t think the 14 yo would be upset by the gift. Perhaps the 11 yo more so, emotions are a little more raw at this age.
However, it’s the symbolism of putting the bauble on the tree. Not only does your dc get to spend every day with their parents together but they now will have a constant reminder of this in the form of this bauble hanging on the tree. And unless I’m mistaken, it sounds as though there will a new one added every year.
Even as an adult, it would make me feel left out, excluded from my father’s family home if this were to happen.
It is very true your dh can go out alone and purchase a bauble for then each. It has been suggested to you that you do this together as a blended family to symbolise to the older 2 that despite not being their mum, you are all a family and they are very welcome.
I can understand why you’re saying the bauble is irrelevant. In the scheme of things, yes. However the symbolism of what it represents is the issue. If you want a happy and harmonious home, I would listen to the people trying to explain this to you.
Teens do seem very big when your child is small. But teens are nowhere near adulthood, still needing a lot of love and guidance. And they are incredibly sensitive, perceiving the smallest sleight. Telling their dad he can sort it out cos they’re not your problem could be the start of a real them and us situation.
Even if simply the sake of you marriage, to avoid the possibility of parenting alone and to prevent your child from going through the pain of parental separation, I would listen to what your dh is telling you.
I have no skin is this game btw. I was neither a step child with half or step children nor have stepchildren of my own. I do, though, know what it is to not v treated the same as my sibling. And it hurt. Deeply.