What would you do?

I think it is nobody’s business but your own, but food for thought from your friend.
How is it unfair if you are treating your children equally?
It could equally be said to be unfair if you gave more to those of your children who have offspring.

You don’t say how many children you have, which may be relevant, nor what sort of amount we are talking about.

Another way of looking at it is to treat each of your relatives as individuals, dividing the total between them ie 7+? Though it will need to be put away for the under 18s.

Are the older ones sensible or would they just blow it?

Do you have a specific reason to want to give money away just now? Be aware of rules around Deprivation of Capital.

Inheritance can be challenging. I usually feel it’s better to leave any inheritance to the next generation, that is our adult children. It’s your choice though and one I don’t believe you should be criticised for.

If you want to give your grandchildren a gift now I don’t see that isn’t fair on the childless couple.