DD1's 5th birthday is in the spring. PIL announced over Christmas that they will be on holiday again for her birthday. This will be the third year in a row they will have booked a holiday over her birthday and therefore missed it. AIBU to think this is quite hurtful? I could have understood occasionally having to miss her birthday for a holiday, but 3 years in a row feels a bit much.
There is a backstory here in that me and DH feel that SIL and BIL's children are favoured by PIL over ours, and I can't imagine them ever booking a holiday over one of our nephews birthdays, so this may be clouding our judgement a bit.