I have 4 boys, and try to keep it roughly even on both money and number of gifts. If it varies a little I'm not too bothered, but I wouldn't like one to have say 10, and another to have 20 you know?
Last year and the year before DS4 was too small to really know so his first Christmas he had maybe £50 max spent on him as he was only 2 months old. Last year he had about half the other boys budgets but this year his will be the same as theirs.
I spend about £300 each on them which I know might seem a lot to some, but they get maybe 3-5 presents for their birthdays, I don't buy them toys the rest of the year, they have to save their own money for anything they want, and I think that as long as you raise them right all year, 1 day of spoiling isn't going to hurt.