Every week on here there is a thread saying inheritance should be split equally between the children.
I’d imagine they are doing a version of this - £100 per family to be split between the grandchildren - be that one or 10 per family.
I think the difference is that Christmas gifts are just that: gifts, whereas an inheritance is not a deliberate gift but rather a way of distributing money and assets which can no longer be used by their previous owner.
Also, inheritances tend to be a substantial amount of cash whereas Christmas and birthday presents aren't usually worth life-changing sums.
The other consideration is that Christmas and birthday gifts are usually given every year and adjusted according to the circumstances of the giver and receiver, whereas an inheritance is a single one-time transaction.
When you die, you know that you've had all of your children but you have no way of knowing that all of your grandchildren have been born (or adopted), especially if you have one or more sons. There was a thread on here some time ago where an elderly man made provision in his will for private education for his two GC (by his elder daughter) and named them for this in his will. He then died and, later, his younger daughter (who had previously thought that she never wanted children and had told her family as much) had two children of her own. There wasn't enough money in the will to pay for four children's education, but even if there had, none of it had been willed to the younger GC by name - of course it couldn't possibly have been. It caused a greatg deal of lasting distress to the younger daughter - not just the loss of education potential, but the unfairness.
Your in laws are passing money on to their kids’ children, not necessarily their grandkids, that’s the difference.
That's what I thought too. You would hope that they would love them and want to treat them because they are their grandchildren - individual loved members of their family - and not merely because they are their own children's children.
Would they allocate things like babysitting this way too? Not do it on a basis of need but look after their 'only' GC twice as often as their cousins who have a sibling? What if they had a child with children and one without - would they refuse to babysit the young children on the grounds that they never babysit for their other child whob has no need for a babysitter?
Food on Chtistmas day, if the families all go to them - a great big plateful for the 'only' GC and the same amount divided by two or three or whatever for their cousins?
We're in a similar position, having one child whilst my SIL & BIL have three. I'd be very upset if our child was given three times as much as his cousins, just because he has no siblings (and already three times greater proportion of our time, attention and family resources than his cousins do in their immediate family anyway) . His DGP have four GC and they split their (very generous) GC birthday and Christmas giving four ways, which is exactly how it should be.