When D1 got married, the cut off for plus one was if they were engaged or living together. They made special allowances for my niece and nephew because they grew up together (went on vacations few times a year and spent every Xmas together).
When my only niece got married this May, she sad no children were invited. D1’s baby was still getting breast fed and the wedding was a flight away. The groom’s side also had few babies, but they were all within a driving distance to the wedding. D1 ended up bringing the baby, but her husband couldn’t attend the actual wedding because he had to babysit the baby. D1 could have made a choice of not attending, but she she didn’t want to miss her cousin’s wedding. I am still speaking to my sister, but there is just a bit of frost.
My brother’s sons are planning their ending for next 2 years and my sister’s son and wife are getting ready to start a family. Wonder what my sister will say to my brother when the time comes.