You can either go to them or they can come to you.
This is not for those clients on a budget, so don't under price these things. The labor, packing, packing back up, the time doing the party, and the big one... CLEANUP!!! And then there is the cleanup of equipment when you get back. These parties must be about $15.00 and up per child with about a 12 child minimum. That would be for box mix cupcakes and shortening based frostings with sprinkles and piping bags. This is below what I charge. I also have a fairy tea party that runs about $35.00 per child. I can do this at my bakery. Mobile is another story.
I have sundae glasses with little serving spoons for toppings. Boxes to take home their creations is also a must. I give two cupcakes, one to eat, one to take home.
Sweet frostings in colors already in bags will work. Two cupcake flavors or one will do. you also need a topper to finish the look. I use squares of wax paper to demonstrate the technique of the swirl for older kids and then add the frosting back into the bag. For little kids, already frosted is good.
I do buffets and handle the whole process from fabrics to flowers. I also have for rent everything for a shabby chic event (weddings to photo sittings). Most of what I need, I already have. But you will want a look and a complete package, maybe playful plastic tablecloths, candy jars or bowls for toppers, and the sundae cups for sprinkles.
Be sure to have a total look so that you can publish the pictures. I'm guilty of not having my buffet photos up yet, but I do have plenty of photos.
Once you have a few on your site and position them to come up in a google search, you will get inquiries. Do not advertise without the price. This is one where you will get inundated with calls from those who can't afford them.