Up until you reach a certain age or place in life birthdays are a big deal, and they should be a big deal. Even after you reach that stage in life (adulthood or parenthood) when your birthday is treated differently by those family and friends around you, I still think you should do what you want (within reason) on your day. We can call birthdays the ultimate Daily Vacation day. Sometimes, however, things can get in the way of planning your day the way that you want.
My birthday is tomorrow. I am 2 months pregnant and right in the middle of my first trimester queasiness. I also have a 6 month old with a cold. Fortunately, I can still function fairly normally with my morning sickness, and I have a daughter who still laughs and smiles most of the day despite a runny nose. Unfortunately, I was hoping to spend a big part of the day at a park or maybe even drive to the ocean for a few hours. Even if your child is a happy ill child, she is still an ill child that can't spend a crisp autumn day at a park or the ocean. So now I'm left to figure out how to make my day special indoors.
It helps when the unexpected shows up a couple days in advance of your plans, so you have a little time to work with it. Don't be discouraged when something gets in the way. Instead, reassess and replan and go from there. Perhaps you can't do exactly what you wanted, but a variation of the original plan might work. Or you may have to toss it all away and start from scratch. Don't give up on your Daily Vacations because of set backs!
As for myself, I still don't know what I will be doing tomorrow, but I'm making sure to clean the house today, so that I won't be hindered by "have tos" once I decide on my "want tos". And you can be sure a big HAPPY BIRTHDAY banner will be tacked up in the house all day to remind me that despite the unexpected, this is still my day. What will you do with yours?