If you have kids, odds are they want a pet.  You could consider a Hamster or Parrots, but I would recommend starting out with an aquarium.  Aquariums are great for children to own, since they help them to learn responsibility.  When your child owns an aquarium, they must clean the tank, feed the fish, and keep the water clean. 

An aquarium does not cost a lot to keep, and the child could even help with the little costs associated with the aquarium.  Food for the fish is inexpensive and lasts for a long time so long as the children don't over feed the fish.  Some aquariums require filters, and those don't cost a lot either.  Odor is not a problem unless the aquarium doesn't get cleaned for a long period of time.

Children will have fun looking at the aquarium fish, and most will even like cleaning it and caring for it.  All kids love to feed the fish, so you don't have to worry about them forgetting to feed them.  If anything, they are more likely to overfeed the aquarium fish.  The kids definitely like to buy pretty plants and decorations for inside the aquarium too.  Aquariums are a great hobby choice.

All in all, kids like fish and aquariums and learn a lot taking care of them.