You can purchase Mickey Mouse invitations from online vendors or your local drug store, department store or party retailer. You can also make your own.
Use a photo of your child with a desktop photo-editing software program, like GIMP or Adobe Photoshop. Simply superimpose a black mouse-ear hat on top of your child's head. If graphic design isn't your thing, you can use scissors to cut a pair of mouse ears from black construction paper and glue them to a photo of your child.
Make enough copies of this picture for each guest. Glue them to the front of a plain, blank greeting card. On the inside of the invitation, write "Mickey and I are ready for fun. Help me celebrate as I turn one." Also include all of the party details.