Easy, Cheap activity with kids.

One activity I suggest if you have small children is birding. I've just started watching birds a couple months ago by watching the birds in my front yard. The best thing about birding? It's free. Well, practically. You may want to get some binoculars (I got some at a CVS for $9.99 which were 7x magnification, and which is great.) Then get a cheap bird reference guide, and you're pretty much set to go. I've been able to identify at least a dozen or so species in my own yard. Previously, they had been classified by me as black birds and not black birds. It's very impressive when your 3 year old can tell grandma that the bird outside on the rock is a mourning dove, because it's gray with gray spots.
Put some birdhouses/birdfeeders out. You can get simple ones from Michael's craft stores for about 5 bucks, or make one easily. I have some large rocks in my front yard and I put bird seed on them, especially black sunflower seeds. The birds will continue to come back once they know it's a spot they can count on to find food. Or just put stale bread crumbled up. This really can be a fun activity that the whole family can participate in. Pretty soon, you'll find your eyes wandering upwards while driving when you catch a glimpse of a large bird gliding overhead. "Hey kids, look, it's a hawk!" It might be a big crow, but at least the kids are getting interested in nature. The most interesting realization about birds in the northeast I had is when I realized that there are buzzards around. I saw a particularly large bird once, said to myself "why, that looks like a buzzard from the shape of its head and neck" but dismissed the idea since vultures only hover around the skulls of long gone cattle in the desert while a tumbleweed rolls by. Some time after that I got hold of a reference book and lo and behold, I confirmed that turkey vultures are local inhabitants. So, the long and short of it is, birding is a cheap, accessible hobby that parents and adults can do, even if just casually. Take a look at my picture of a flicker. Of course the bird watching got me to convince myself I needed to replace my ailing camera....but hey, I didn't even know a flicker was a woodpecker until I started paying attention to the visitors to my yard.