Beside that you must make a instrument safety for your children. Use materials which never make your children hurt. Don't use if your materials contains poison and many materials like that. You can use a safety materials like wood and bamboo. If you use bamboo please make it sure that it can't hurt your children.
Okay to make a shake musical instrument, you need this material like a bamboo, rice, paper and knife. After you ready with your materials now first step you need cut down your bamboo, maybe you need 5 cm. And you must know that children have a small hand so don't use a bamboo with a big width. Adjust the diameter of bamboo with diameter of hand grip. And then fill your bamboo tube using rice half of tube and then stopper using paper. Now your musical instrument for your children ready. Don't think that this instrument very bad, because any music can affect your children. Don't give value from the price but give value of benefit.