Can Scratch be used effectively for children between age 4-6?

We are starting a Scratch course in Hong Kong and whilst we do teach the technical skills of basic programming, we really want to use it as a tool to help our students learn more "soft skills" through team projects/discussions, presentations, analytical and logical thinking, creative design, conducting researches, etc.

With this in mind, we are designing courses for different age group and one of the ideas is to really push the limit and introduce "Scratch" to students at really young age.  In Hong Kong, children attend playgroups as young as 6 months and they are often faced with tremendous pressure to "perform" in school interviews - yes as young as for kindergarten admission!

So one of the goals is to use this opportunity to help students prepare for those moments whilst making it fun through Scratch.

We want to reach out to the community to see whether anyone has any experience in pushing Scratch related course to children at that age (4-6 - or may be even younger!)?  If so, how effective was it?  What are the key challenges?

Many thanks!!