I'm curious, do your kids know what a birthday is? I'm guessing this is less of an issue if they've already just celebrated one. We're not doing particularly well with the whole birthday concept over here. I think she thinks a birthday is a person. Or a thing. She gets that it's associated with presents and cake and balloons etc etc... but since we keep telling her that it's "coming soon" or "not here yet" when she brings it up, she thinks it's missing.
She even had a nightmare about it yesterday. Woke up bawling, saying her birthday was missing. Pointed accusingly at me saying "you find it!!!" I tried to tell her it's just a special day, etc, etc, but no, she suggested that I "go Costco and get it!" Right. And she keeps looking out of the window expecting it to appear. I'm afraid she's going to be disappointed when she wakes up on her birthday and no special person/ thing materializes!
Re: lost her birthday
I'm impressed what a little smarty!
Oh, and no way does mine understand the concept of time either. Which is why explaining that a birthday is a special "day" is so darn impossible. She gets that she's one and will soon be two though, but obviously not in any real sense.