Mix equal parts of borax and powdered sugar. Sprinkle it on ant trails or fill a small jar lid with it. The ants will take it back to the nest and eventually kill the queen. While borax is safer than most chemical treatments, it is still best to keep it out of reach of kids and pets.
Pepperment EO is great at covering up an ant scent trail. I generally put a few drops at the entry point. I have also used a drop or two to break up massive trails across the floor or wall. It's best not to get this on your skin due to it's strength but the amount used is so small that it generally doesn't present an issue. At least my children have never taken an interest in it!
DE is my latest find and so far I love it. Not only has it been effective at stopping the invasions but it is completely safe to eat, provided you purchase the food grade version. In fact, when taken as a supplement it offers numerous health benefits. It can't get much safer than that. To use, simply sprinkle it along the ant trails. It takes some time to work but it eventually does the job.
If you have any tips or tricks to add, please let me know!