Dear Twilight Sparkle:
The cakes? Fit for anything? Please, they're earth ponies, and we all know that the only thing those are useful for is taking the jobs that no self-respecting pegasus, unicorn, or alicorn would want to do. Jobs like picking crops, working in sweatshops, cleaning our facilities, and other menial work.
Oh yeah, and maybe some superior races would be willing to pay earth ponies for sexual favors. Sure would explain why Mrs Cake's children look nothing like her husband.
With that in mind, it confounds me that you'd show any concern for the cakes, Pinkie Pie, or Mrs. Cake's little bastards. Or maybe you just wanted to take the useless foals under your non-existent wing to show Pinkie just how much better you are? I'd certainly understand that, I do it all the time.
Then again, maybe you just got tired of everypony being high whenever they talked to you, so you were trying to prevent her from raising the next generation of drug traffickers?
Ultimately it doesn't really matter, because those two live with Pinkie, so they're pretty much guaranteed to grow up to become junkies. Knowing that, the Cakes probably should have kicked her out before Mrs. Cake gave birth. But then again, they're just dumb earth ponies.
Your totally drug-loving former teacher, Princess Celestia.
Dear Pinkie Pie:
I have some news that might surprise you. Last week, while high on pot, you had an orgy with the Wonderbolts. As a result, you're pregnant.
Your never virgin Princess, Celestia.
P.S.: Please tell your male caretaker (uncle?) that he needs to watch his wife more closely.
P.P.S.: Twilight has informed me that you may be unfit for motherhood. Have fun!