A wooden gear clock would be a great challenge, I could probably get half of that done before I moved on to another project

Toys are always good. It is great to see a kids face light up when you give them something special.
Maybe a game would be nice. Remember the old tabletop hockey games, someone should design one of those. A marble maze would be good too, along with a marble pump to get the marbles to the top.
There is still a week left. SHARPEN YOUR PENCILS!