You're going to need a water gun and a couple of pingpong balls and draw a finish-line with chalk. Have kids "push" the ball towards the finish line. Another great adaption is to use a straw in the bathtub, to push the ping pong around in the bath tub.  
(This is a great idea from therapy fun zone, feel free to look around at other great ideas they have)

This is a great way to have kids and adults work on their pencer grip as well as hand-strengthening in general. Cut a slip into an old tennis ball and have kids push the slit open to put marbles into it. You can paint some eyeballs onto the ball have the "monster eat". To make it a little easier, for kids who can't grasp the marbles well, have them place some popsicle sticks into the ball. 

Remember the game "memory"? Well, this is the same concept, but with noises. You can fill old film cans with rice, beads, jelly beans, etc. and have kids see if they can match the noises! Great sensory activity.

A great idea from moneysavingmoms blog! Get a noodle form the dollar store, cut it up and have your child bead them, this could even be done in the bathtub! 

Save your toilet paper rolls and go find some twigs!! Actually, you can also do this with bottle caps, pompoms, crayons... etc. This is a great way to help kids learn how to count. Make it extra challenging by having the twigs at one end of the stairs and the buckets in the other, so they get a workout at the same time. :) Other great ideas can be found on pinterest.com

Turn off the lights and turn on your flashlight. Have your child try and place their finger on where the light is flashing. this is fun and inexpensive way to entertain your child while having them move around. You can make it more fun by having them place an "easy to take off sticker" wherever the light hits. 

Practice the "ironing board" in the pool. Having kids relax as they float in the pool helps them gain confidence in themselves and in their capacities in the water. This is also a great way to stretch them out and sway them to have the water stimulate their skin. This can be very calming. 

Yoga can be challenging for some kids. Doing hand-over-hand or adding a funny story to the mix can make it all the easier. For example: "Downward dog" is suddenly "walking like a bear". 
The more fun it is for kids, the more likely they are to stay engaged and follow along.

Have kids use rulers and measuring tape to measure things around the house. This can keep them entertained for quite some time and make sure they're engaged at the same time. It's a great way to practice math as well as identification. Want to make it a little harder/ more educative? Have the pictures with words in another language, for them to learn. Try Spanish or French!

Put some colorful clothespins onto the swing and have your child move them from one side the other. This is great for their fine-motor skills as well as coordination. Add an element more by having them do it while they're on the swing. This will give their core a nice work-out at the same time.