This is a sample. Yours is written for your child from the details you give us.
Dear Mia,
Ho ho ho! It is snowing sideways at the North Pole today, and I am writing to you with a mug of cocoa and a very sleepy reindeer snoring beside my desk.
The elves told me some wonderful news about you. You learned to ride your bike this year, and you did not give up, even when it wobbled. That takes real courage, Mia. I also heard how kind you are to your little brother. Kindness is my favorite thing in the whole world, even more than cookies.
And you tried broccoli! Mrs. Claus clapped so loudly that Biscuit the workshop cat jumped off her chair.
I loved hearing that you are dreaming of a red scooter. I will see what the elves can do. Until then, keep being exactly who you are.