It does hurt to see those pictures but our children didn't ask to be put in this situation and it was their holiday too.
Way back when my XH used to come and show the kids the pictures of the all the holidays he and OW were taking. As hard as it was I put a stop to it by simply asking to look at the photos myself! On the one and only occassion I had to do this XH couldn't really say no as the kids were all there. I looked at the photos, made positive comments about them and then gave them back. He never 'volunteered' to hurt my kids like that again!
Mow that XH has the new baby I actively encourage D14 in particular to share photos of her new sister with me. We both found it hard at first but now she knows that she is able to speak to me about the baby if she wants to without me breaking down into tears. The main reason I am able to do this is b/c the new baby looks absolutely like my 3 children My children will never be able to deny they belong to each other b/c they are all so similar but this child is completely different. For clarity I am not suggesting my children would want to disown thier sibling I am just saying that for me b/c she looks nothing like my children I am able to view her as just another baby.
Me 43 XH 45 M 2.7.88 Divorce 7.10.09 Kids D20,S17 & D15