Attach a piece of cloth, a bandana, or an actual flag to the end of a rope or PVC pipe (or both). Drag the “flag” around the yard and let your dog chase you. This is great to play with kiddos who also need to exert some energy.
Sometimes, the short legs of small dogs can’t go very far, but they still love to walk. In my own home, we take a wagon (or Wag!-On) along for the journey. We pull our little Yorkie inside of it when she finally tires out. This can be great exercise for the entire family.