Hydraulics and Pneumatics are great topics to teach children. First of all both words sound very impressive and when the children learn these words they will sound very important and knowledgeble if they use them. Also, hydraulics and pneumatics are used in many machines and in many everyday applications, therefore it is easy to show the importance of understanding these topics. One can easily show and explain the difference between hydraulics and pneumatics - a great "Compare and Contrast" analysis. Thirdly, there are many fun and impressive experiments that can be done with hydraulics and pneumatics in a very inexpensive way, with very accessible materials. And finally, since hydraulics and pneumatics is so useful, there can be multiple projects that children can actually build themselves. Thus weaker students and stronger science students can both do projects, yet with differing complexity.