I have two children (out of ten) with the same birthday, eight years apart.
I agree about not naturally perceiving math ;-).
I have 3 kids. All boys. The first 2 were born on the same day. 3 years apart. A good friend and her sister were born on the same day 2 years apart. WHAT ARE THE ODDS!? Oh about 1 in 365...unless its leap year.