The trick is to give them a tree pruning chain saw, one intended for climbing tree loppers to use one handed - it's an ideal weight for nine years old to use two handed.

And to supervise.

As tested on my children and grand children.

Also, if you happen to have a furnace with a large pot of molten glass, five year olds are capable (given a stand) of making marbles from the furnance and will do that for hours if you can spare the time to let them.