I inherited a similar amount when my Granny died, I wanted to put some away for a rainy day, have a holiday and buy a piano and a second hand car.
But when I received it, DH wasn't getting any work in (self employed and just returning to work after an accident, so had to build up a client base again as he was off for over 18 months).
I couldn't justify using the money for all the luxuries the family would have heartly approved of, we needed it to live. I was also pregnant, furnitureless, and about to be made redundant (fantastic timing!) and were moving house. So I spent it, all of it, wisely and carefully and extremely gratefully. I hope my Granny would be pleased she could help, I think she would.
My mother has never let me hear the end of it, she makes 'jokes' about how shit I am with money (true sometimes, I don't much care for it so long as we get by) and how I 'frittered' the inheritence whilst my sister still has all of hers (my childless sister who's married to a wealthy, a lovely, man).
Water off a duck's back. You shouldn't have revealed your intent, but now you have, you'll just have to wait for your dad to stop sulking and have a real conversation with him. Tell him that YOU are saving for your children's future, and that your relative has given them a better standard for the present, a gift you appreciate deeply. Then ban all talk of it in future.
Tell him you've considered his view, and will be accomodating his wishes to a large extent (you already are) but don't change what you are actually doing, just rephrase it.