Chickens need housing to protect them from foxes, and ideally they need a grass-based run on which they can be "rotated" so they don't scratch it all up. Depending on the breed, each hen can produce 100-300 eggs per year, so you'll need a few if your family has a serious egg habit. And in case you have neighbors who are horrified by the prospect of hens clucking around the garden, you should stress that chickens are unobtrusive, don't smell and make little noise (as long as you don't have a cockerel).
The quality and taste of home-laid eggs has to be the big attraction. Also you know what the chickens eat and how happy they are, after a while you will think of them as pets as they all have there own personality
Getting set up with chickens can be very cheap: the birds themselves cost from £15 to £25 each for point of lay "approx 20 weeks old" and the housing can be home-made, although a wooden chicken "ark" will cost up to £200.
Chickens make excellent pets for children. They are friendly, comical and affectionate plus they provide eggs too.