I know what you're saying: That's so nice. You might even draw out the nice, like niiiiiiiiiiice. Now you're saying: Whatever, shut up.
In fact, I go and get the flowers myself and put them on the table and give the birthday boy a big hug and say: Thank you for the flowers. It was so sweet of you to remember that this day is as important to me as it is to you (possibly more so, and certainly more memorable because of the "natural childbirth" and all) (I don't say that part out loud).
Hopefully they'll take the hint, eventually. But they're boys, so what are the chances?