My son, aged 10 wants to learn how to build flash content. Starting with some simple animations and eventually on to games.
Are the any free/express tools available for this sort of thing or is the only option an expensive software package from adobe?
If your son is into development then you can use FlashDevelop ( a windows only IDE ) to develop your flash content in pure AS3. Adobe make available the FlexSDK for free which has the required compiler that the IDE requires to compile.
If he wants to use the timeline, then personally I know of nothing free.