Invitations: You can see some of them taped around the table edge in the above photo. I drew and colored Cat's Hat on cardstock with Sharpies, and then copied it onto more cardstock. Then on the back I printed out the details of the parties. I made extra copies of the hat to use as decorations.
Other decorations: Red and white balloons and tablecloths. I took all of the Dr. Seuss books we had around the house, as well as borrowed some from the library, to place around the house. And I took empty oatmeal canisters, wrapped them in red and white construction paper, making Cat's Hat to use as balloon "anchors".
Food: It was a mid-afternoon party, so I kept the food to just a few snack items. We did goldfish, which I served in a round fishbowl. I also drew Cat's fish onto cardstock and taped it to the bowl.
Then I had to have green eggs. For these, I took white chocolate covered pretzels (I used Flipz), filled in the holes with white decorator icing, and then pressed a green m&m into one of the dabs of icing. These were really yummy and didn't last long!
I had a cake for my daughter, in which the bakery used my invitation drawing to put on the cake.
And for the guests, I made Thing 1 and Thing 2 cupcakes. I made red velvet cupcakes. Iced with white icing. Topped with blue cotton candy.
As a keepsake for my daughter, I picked up Dr. Seuss's Happy Birthday To You book and had all the guests sign inside.
My favorite part of planning a party is doing the favors for guests. For this party I had 2 favors. The first were sugar cookies that were shaped in the letters of each guest's first name. I then attached the corresponding verse from the ABC book. Big M, Little m...etc.
I also took red and white craft felt, sewed strips of it together, and sewed them around baby food jars. Then I took a heavy wire, and curled an end to make a photo holder. I anchored the wire in the baby jar with hot glue, and glued on a circular disc of felt on top to hide the inside. I used these photo holders to display photos of my daughter, one photo for every month of her first year. When the party was over, I took out the photos and gave the photo holders to the guests.
And that's it! Dr. Seuss materials are often found in Michael's and teacher supply stores, so there's lots more you can do for this themed party.