I have been working on this for a couple months now. Here is what I have come up with and what I am doing. I am putting together a christmas reveal for our 3 grandkids. I ordered 3 card stock owls from etsy. You put together and they hold the hogwarts acceptance letter in their claws and I will hang them in front of xmas tree using clear fishing line. The envelope has an acceptance letter to hogwarts, a school supply list and a ticket to platform 9 3/4. The envelope is addressed to: childs name, Under the christmas tree, my street and number, my town u.s.a. (fill in the real names etc) it has owl post and wax seal. Looks very official and the I think the hanging owls will look great.
Then, under the tree, each child will have another very official looking package with HP markings, ministry of magic stamps, packed by house elves seals etc. in official looking brown distressed kraft paper. Inside the package, each will have a cool old looking wood box from hogwarts with an awesome potion/supply kit inside. The potions will really work! The two 10 yo kids will get an awesome book I found about all things HP and the non reading 7 yo will get a HP poster and map set for his wall. All of them will get a cheap plastic light up "practice" wand and chart of wand motions, for them to practice with, plus some other cool HP tidbits I have been getting for their potion kits. I will tell them that the Ministry of Magic does not allow shipping of powerful magic items such as wands and we must wait to get the real ones at Ollivanders when we go. I have tried to keep in as authentic as possible. I will post pics here as I assemble this. And I will post links I have used.