I have a good relationship with the oldest SS (turning 23) except that he pretty much stopped visiting us a few years ago.
Until a few years ago, he was still congratulating me with my bday, when he stopped, I continued anyway, I figured that hes not into that and theres noone to remind him.
Well, last year, he called my DP to ask about the bday of his exSM (separated about 9 years ago) and I once heard him saying that he remembered her bday date. The exSM didnt raise him or anything, but SS is friends with her son and she made big efforts to be extra nice with SS calling him her love, etc, so obviously hes more connected to that family.
Im not jealous, but I figure that if he can make an effort for his fathers ex wife that he considers his family, he could have asked his father about mine or my children`s (one is his half-brother) if he wanted.
The question is should we acknowledge his bday? At some point, I figure its like with friends who dont make efforts, you let them go...