Yes.
And how about when Granny gives money for other days out or celebrations that have additional costs?
Granny giving money towards a prom dress, exam results, or a wedding dress?
Should the GDC who aren't spending the money on a prom, haven't passed exams or buying a wedding dress get that cash to spend or whatever they like? Because that's fair?
Then what happens a few years later when it IS their prom or wedding? Granny gives all the DGC the same amount of money again to make it fair?
Or does Granny say, well, you had that money years ago, you all got the same amount of money so that's fair?, or does Granny give more to the person who already had the money for a prom or wedding, because they spent it on not a prom or a wedding and then Granny has to give it AGAIN to that GDC, and then again to all the other GCs who aren't having their prom or getting married?
And then the same process happens at the next prom or wedding?
Grandparents aren't ATMs and they have no obligation to do things fairly all the time, because sometimes, doing things fairly as in giving everyone the same amount isn't fair at all when there are different circumstances on different days.
Fairly doesn't mean equitable, and that's important here. There's nothing fair about everyone being treated the same, because it often isn't fair. Equitable treatment is more appropriate.