My mother has 5 grandsons (now all grown adults), but there was a 7 year gap between the first 2 (both mine) and obviously, as the first was initially the only one for many years, he was totally spoilt. But then along came the second and she 'acknowledged' his existence, but never really wanted a lot to do with him.
Another few years passed and along came GS no 3, followed another few years later by twins (all from my sibling) whom she was more involved with, but definitely not to the extent she was with the first GS.
She's been known to only tell people about her 4 GSs (not the 2nd, which came back to bite her when he did some work experience at her place of work because she never said a word about him), but the 1st always has been, and still is (now mid 30s), her admitted favourite.
Thankfully, my second son now doesn't care that she's not interested in him, but he was very upset about it when he was younger.