If you can arrange some glasses or empty jars then fill them with different amount of water. Arrange them in a sequence and then ask your kids to strike them one by one gently with a spoon. They will definitely enjoy the variety of sounds coming out of every glass.
Do not get surprised as you can make even a guitar at home. Get an empty shoe box and remove its cover. Now stretch rubber band around the empty box. When rubber bands will be plucked, the hollow space will create sound. Do not forget to make arm of the guitar. You may use a broad stick or ruler for this purpose.
Another easy-to-make instrument is an acoustic horn. Paper towel rolls that people usually dump can be an ideal material for these horns. All you need to do is to seal one end of the roll. You may use a plastic sheet or piece of wax paper for this purpose.
After securing the end, start punching holes on rolls with a thin-edged pen or pencil. Remember, these holes are to be made along the length of roll. Now, your children can blow into this horn and make different sounds by moving their fingers on the holes.
If your kids want you to make some strong beat instrument then you should go for the drums. Do not worry; they are as easy as any other musical instrument. Pick empty oatmeal boxes; make holes in the middle of both ends. Next thing you need to do is to pass the thread through holes of drum and it is ready to be handed over to your children. Give them something to use as drumsticks, old chop sticks may be.