I am agreeing with Notanan2 again today .
I wouldn't want people to know I had hundreds of millions - it would totally change everything, whether I wanted it to or not, so I approve of the white lie idea. I might extend it to saying that I had a fixed sum to share amongst the family, and would give it to my siblings - they could decide how to share it amongst their own children, as I wouldn't want to get involved in any disputes. The only strings attached would be that they would have to agree to keep the source of the money secret - otherwise it would be up to them what they did with it.
I would love a house with a sea view, and I would like to fund an Arts Centre in my home town, and give performance and exhibition space to up and coming artists of all types. I would also offer sponsorship to local poets, artists and musicians - something like the fees for an MA and a salary for five years after graduation so that they could concentrate on their art without worrying about the rent.
I wouldn't give massive sums to my children, as I think it would stop them from finding out who they are and what they want from life. They would get the lot when I go, and in the meantime I would give them a monthly income that would replace a reasonable but not wildly extravagant salary (£40 or £50k a year?), so they could decide whether or not to work, but not have enough to swan about on yachts or bath in champagne if they decided not to. I wouldn't tell them that they had riches in store either, unless something huge happened and they really needed to know.
After that, I would like to do something for the homeless, but I would have to take advice, as I know how easy it would be to do more harm than good.