When my boy/girl twins were 3 we had a dalmatian party. When guests arrived we painted their face like a dalmatian with a face paint pencil - black nose and spots on the cheeks, and put on ears we'd made (bought headbands at the dollar store, wrapped 2 pipe cleaners in ear shapes, and hot-glued white felt to ear shapes, front and back, then used black sharpie to put black dots on felt ears). Then we took a polaroid of them. We taped the picture to a frame we'd made out of white posterboard that was doghouse shaped and stuck a magnet on the back. The kids then decorated the frame w/ dalmatian stickers while we waited for everyone to get there.
For games: Kids rotated carnival style through 3 games and won a small prize from each - dalmatian pencil, stickers, etc. I'd bought the plain white bags with handles at WalMart and drew a giant bone on the front with their name, and paw prints all over. Kids collected their prizes from each game into the bags.
Bean bag toss: I drew a giant picture of a dalmatian with a big open mouth, and stapled it to plywood and cut out the mouth. I made the bean bags out of tan felt into bone shapes.
Bone find: this was the longest prep - I cut out 100 dog bone shapes from posterboard and hid them around the yard and kids got to retrieve them - they loved this.
Pin the tail on the dalmatian: drew giant dalmatian on posterboard minus a tail, cut out enought tails to be stuck on with tape.
Then we had a Dalmatian pinata
Treats: I bought two-sided dog bowls and decorated them with the kids names and pawprints. Served cake and ice cream in the two sides of the dog bowls.
Two cakes because each kid needs their own cake - one dog shaped, one bone shaped.