Need childrens' stationery that I can edit with letters and symbols

I am trying to create encoded messages for children to de-code as a game and would like them to be on themed stationery. I need help with 2 different parts. First I need help finding or creating the actual stationery and 2nd I need help figuring out how to edit the stationery to input the coded message. The stationery itself can be simple- I'd like to have about 5 different types, each with a different theme (Christmas, birthday, animals, cars, princesses). I imagine editing the code into the stationery might be the difficult part. I would like to be able to have 3 different types of codes, one will use only letters and normal punctuation so that should be simple but the others will use Morse code and Pigpen cipher so I will need to be able to input symbols that are not readily available through Word. I uploaded samples of a Christmas-themed stationery that shows what I'm looking for and also a hand-written Pigpen cipher so you can see the types of symbols I would need to be able to input into the stationery. Please contact me with any advice you have on how I could accomplish this. I'm not very computer savvy so it's hard for me to estimate how difficult this will be to put together or, therefore, how much it should cost so please give me some insight on this, also.