Just Add Water
Let's say you have some weeding to do, so you need to keep the kids busy outside for an hour. (Or let's say it's been an embarrassingly long time since you weeded, and you need two hours. That has never happened to me, mind you.)
Of course, the best idea is to have them help you. I have found that inexpensive disposable gloves work well for little helpers, and it's a great learning experience and it is fun to work together. However, I can pretty much guarantee you that your kids won't want to help you for the whole one (or two) hours. In that case, here is something else you can try.
You will need one small waterproof table, one large bucket, and several small buckets, scoops, and cups. Fill the large bucket with water (preferably from your outside faucet, so you don't have to carry it far). Place the bucket and your appropriately-sunscreened little darlings in the vicinity of the table and watch the fun happen! (Disclaimer: Please remember that small children can drown quickly, even in buckets of water, so only do this if you are going to be weeding right near them and can supervise appropriately.)
My kids entertained themselves very happily this way for two (I mean one) hours this morning!

