Oooh, that's a good one Glaikit!! I love it.
Could you do the cake like the mad hatters hat maybe? Although a cake stand with cup cakes would probably be more in keeping. Could you make one out of more mismatched tea sets? Glue together plates of ascending sizes with tea cups between the layers to make a sort of higgldy-piggledy cake stand?
Lots of bunting for decoration? I'm sure you could make some (or get some made) with "Happy Unbirthday" on.
Croquet as you party game is the obvious choice.
Invitations with "Please do not be late for a very important date..."
"Welcome to wonderland" sign on the back door as you take the gusts through to the back garden.
Small rose bushes to decorate the table?
As well as normal sized mismatched crockery, could you get some tiny dolls house ones (I saw a chine dolls teas set in poundland last month) and a couple of those huge, planter sized ones to really mess around with the sense of scale.
Put little toothpick flags in the cakes with "Eat me" on and serve drinks in stoppered glass bottles with "Drink me" on luggage tags tied to the necks.
Hide a toy mouse inside one of the teapots on the table.
If you have a tree, you could sit a Cheshire cat - or just a Cheshire cat smile in it.
Fill vases - or more teapots - with flowers from the book, like tiger lilies, daisies, roses, violets, and larkspur
Play "pin the grin on the Cheshire Cat"
You could get 'Paint your own' mugs or plates as another good party game. Would be great for this age group who would probably create something lovely that they'd want to keep.
I found some other great party game ideas too -
Do the Caucus race. Make your guests run around in a circle, and when you shout 'stop' the last one to sit down/run to the middle is out. Or make a caucus version of the game musical chairs, where you remove one of the chairs each round and people have to find a chair to sit on when the music (the caucus race song from the Disney movie) stops.
Make up silly riddles
Play 'Paint the roses red'. Buy some fabric white roses and red paint (or markers). The person (or team) who finishes painting his rose first wins. You could give time penalties for sloppy painting or spilled drops. You could also set a general time limit and have someone dressed as the Queen of Hearts storm into the room when the time is up.
Buy some basic top hats and let your guests decorate them
Hide a small golden key or a White Rabbit plush and have your guests find it
There is loads more stuff here
You could go crazy with this idea, there's just so much to do!!