As a writer, penning a birthday card is oddly pressurized. You're expected to be eloquent in general, but birthdays typically only inspire a set number of sentiments. Of course, writing your own kid's birthday card takes that pressure to another level, especially if you happen to be the kind of person who saves all those birthday cards as mementos. That's why we could all use a little primer on what to write in your child's birthday card, because you want it to be fun and memorable, and that can be tricky.
Wishing your kid a great next year, lamenting that they're growing up so fast, or other such unspecific birthday card messages never seem quite enough for your own child. Instead, try being as heartfelt as possible, and try to remember that the goal is to make your child feel loved and special on their birthday. It doesn't have to be award-winning poetry to convey that you love them, know them, and are glad they are your kid.
Likewise, it doesn't really matter what card you write your message in. My grandmother was so frugal she used to cut the second page out of cards and just write on the back side of the front. I loved them every year.
If your child has a birthday coming up, here are some memorable and heartfelt messages to get you started.