Rat poisons are a bad idea. They pose much more risk to small children and household pets than they do to the wild rats. There are several common forms, including pellets that are supposed to act as bait in their own right, powders to mix with other baits, or little sticks of poison-gas dynamite that you're supposed to detonate inside their burrows (assuming you can find an active one).

Most rat posions contain warfarin or strychnine, although I don't think the former is used much anymore. If ingested by humans, strychnine causes death by constricting the muscles of the throat and/or paralyzing the diaphragm, as well as causing convulsions and gastrointestinal problems. The box recommends emergency tracheotomy in the event of accidental severe strychnine posioning. Your child will never talk again, assuming s/he lives.

Not one rat poison we've tried has proven effective. In some cases, enormous piles of pellet-type posion disappeared, replaced by a smaller pile of rat droppings, many tiny pawprints, and not a corpse to be found. I'm glad, actually...killing the rats sight unseen leaves them to rot and spread disease. This is not a good thing.

Also, I strongly recommend against the dynamite-stick thingies. They are very troublesome to use, and you will wind up breathing fumes, posion fumes, which can't possibly be good for you. Avoid them. They didn't work anyways.