I bought this set of blocks and designs of various contraptions for my 5-year-old boy. I wasn't sure if he will be able to assemble most of those crazy constructions, but:
1) with minimum help and support kids will manage easily
2) some are easy, some are more demanding, so you'll always find something for yourself / your kid
3) the racer and the gondolas are my sons favourite
- the first is difficult but rewarding
- the second is extremely easy and allows limitless adjustments
4) we tried the blender and it blends!
5) when my son went to bed I set for two hours designing more advanced blender and finishing with a model of a gear box to explain the workings of this mechanism to my wife
6) when your kids are away, and you have friends at home, build the time killing machine - at the beginning everyone will think you're nuts, but after you start killing the time, there will be an endless roar of laughing people ;-)
Anyway, this is Lego, so kids will love it and always be able to build something.
You've got 16 different contraptions, so tons of ideas.
The book is extremely well prepared for children and rough handling - thick paper, plastic, spiral binding.
These are technics blocks, so the more you have (or will have) the more you'll be able to do.
The rules are simple, so once you learn them (and search the Net for more instructions if you will) you can build anything! For example a Lego launcher for paper planes ;-)
The only downside I found is the box itself which can be accidently opened by a child. Means a lot of searching for blocks under the table.