Christmas

Assuming the distances are not that different, alternating seems to me to be the fairest way to go, and as you have long lives ahead of you, it's sensible to get into a simple routine that avoids annual disagreements and resentments.
However, having made the generous offer to go with your partner's wishes (even if unexpressed), I suspect that changing arrangements at this late stage will cause much more guilt and resentment, especially if the children have been given a promise.
On the whole, most people would argue the holidays are much more important to children than adults, and as an older adult myself, I know that most older people (though not all!) worry less about such things as we grow older.
Whatever you decide, have a thought for future years, and try to avoid misunderstandings about your intentions. Most relationships work better if each is honest about their wishes - but is prepared to compromise - rather than second guessing the wishes of the partner.