Assuming all birthdays are equally likely, which is probably close to being true (and assuming you didn't rush or delay the births to make it happen!), the probability that your daughter would be born on your birthday is 1/365, and likewise for your husband and son. So the probability that both will happen (assuming you have only one of each) is 1/365*1/365 = 1/133225 = 0.0000075. It's better than 1 in a million, but still rare.
On the other hand, the probability that something like this will happen is considerably larger, because if the two birthdays were swapped you might consider it to be just as surprising, or if both were born on your anniversary, and so on. I know a couple with two sons, one born on labor day and the other on tax day (the father was an accountant). Unusual things happen all the time.
In fact, since there are many more than 133,225 people around, the probability that this will happen to someone is near certainty!
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