Every year for my nephews and nieces birthdays until they were 7ish I would check when (if) they were having a party so I wouldn't miss it.
Now my youngest is 5 we're having her party - just family- in 3 weeks. We did the same for her big sister until she was 6 as thats when she started wanting friend parties. Seeing their cousins is my kids favourite thing in the world.
AIBU to be upset that my sister won't come with her kids, but instead suggests a pub lunch half way (not viable as other side of family coming from opposite direction and not really 5 year olds top choice of party!). She has her (not much liked) in- laws staying but they are leaving after lunch. It's a 1hr20 trip.
I probably am completely bejng unreasonable- but as the youngest grandchild born during covid DD5 does get forgotten a lot. I'm especially upset as my sister made such a big deal when her's were born about the role of an aunt, and how I needed to know her kids well. But she doesn't seem to care too much about mine except when we meet up she's lovely to them but there is no extra effort outside of those general family catch ups.