You can also buy traps full of the stuff that are already (mostly) kid-safe; you snip off the end of a plastic container and set out out. Be aware that there are different baits for different ant types, though. The other way works too, but for a little more money you don’t have to mess with foil.

While you’re waiting for the colony death, few ants will cross a line of ground cinnamon. You can shake a border around a room, and - unless they’re coming up through the floor in the middle of the room - it makes a pretty efficient barrier. It’s cheap, human-safe, and easy to vacuum up after the colony is dead.