I am an avid fisherman, although I don't get to go as often as I would like these days.  I enjoy it because it is low to no cost, can be done with kids, and can provide a tasty meal.

It is a low to no cost activity because the equipment can be bought for next to nothing and used for years (Less than $20 can equip two people).  Check out yard sales good gear can be had for next to nothing.  Saltwater doesn't require licenses.  In-state residents can usually get a freshwater license for less than $20 (no license for 16 and under in most states and divorced fathers need to be current on their child support in some states).

This is a family friendly activity.  The kids can learn how to do it pretty quickly and there is nothing like seeing the look on their faces when they reel one in.  Just be prepared with patience-- early on you won't get as much fishing in as you help them with baiting hooks, casting, and solving problems.

Finally, with successful fishing comes a tasty meal.  Our kids, like us, are spoiled by fresh fish.  We see frozen, dark discolored, and over-priced rainbow trout in the supermarket that I won't feed to a dog.  The trout we eat is usually just hours old.  NOTE: Be sure to check with your fish and game department for any advisories on the fish and body of water you are fishing-- unfortunately, some fish and water isn't safe.

Good luck!