A very simple practical life activity you can give your kid is to have them take measurements.
We have a few redecorating projects on board so I enlisted my son to help me take measurements. He's always playing around with the measuring tape and loves counting the numbers. It was easy to show him how to hold the tape at the edge of the item and pull it taught to find the correct number of inches. I demonstrated how to record length, height and width of an item.
Not only was this a great way to keep him busy while making chores seem entertaining, but it helped me out since I no longer had to use his brother's valuable nap time to complete a few tasks.
... and maybe he learned a few things about how to to write and take dimensions. I suppose that's always good, too.
Of course you don't have to be redecorating to give your kids a tape measure and a pencil. Just let them loose: no fancy instructions needed.