Clean Your House
Something had to attract the ants into your home. Thoroughly clean your kitchen. Concentrate on getting any crumbs and residues off the floor. If this doesn't take care of the problem, move onto some of the other solutions.
These are inexpensive and convenient to use. They are also safe to use around pets, unless your pet decides that it is a chew toy. Place them near where you've seen ants. These traps do contain poison so they should be used with caution.
Mix boric acid in equal parts with sugar. Add some water to make a slurry and spread it where you've seen ants traveling. The ants, attracted to the sugar, will eat the mixture and take it back to their nest. Since boric acid is toxic to ants, the mixture will kill not only the original ant, but any ant that shares in the harvest.
Spread a small amount of baby powder along cracks and window sills where ants enter a home. They won't walk through it, so you've effectively formed a roadblock.
Frosted Corn Flakes
Leave some smashed corn flakes out for ants to snack on. Ants will eat them because of the sugar, but they can't digest corn, so it kills them and any of the ants that eat the flakes. You can also spread it outside to encourage the ants to stay out of your house because they can find an abundance of food to snack on outside.
Ants will be repelled by certain smells like peppermint and cloves. So if you have an ant problem in a closed space like a cabinet, leave a couple of cloves in the cabinet, or crush up some peppermint leaves and leave them there.