This here is another great item for a kids punching bag it is made by Everlast Boxing and Fitness.

It is more durable than all the rest of this style punching bags. The Base is larger and the spring is more durable, it is stronger and the target does not have to be inflated. It is made of Synthetic Leather construction and it is filled with a combination of chosen foams, so that it may never loose it's freshness and never go flat on you. The base weighs about 60 pounds when filled with water. No sand is rquired in this one. Water works perfect! Adjustable from 50 inches to 64 inches high. This kids punching bag can be used by any kid size. It's durability fits all kids even big kids.