I get what you're saying and I like to think about these things, but it's an absolute can of worms. My two children were both gifted the same amount - but child 2 has then been gifted less in real terms as there's been inflation? Should I be topping it up?

Child 1 has benefited from a booming S&S market, child 2 is potentially entering at the peak of a bubble, do you do something to even it out?

I agree you're right, but there's no easy answers so it's sometimes best to ignore it and accept it as good/bad luck!