When you say upstairs, do you mean a second level, or just the main level? If they're on the second floor, that could mean bigger problems, and I'd get a pest control company in soon.
If you just mean main floor and basement, there are a couple of things you could try. First, if you can figure out how they're coming in, try blocking it up. Caulk the windows, make sure door frames fit tightly, try to cover all the holes (this will help with insulation as well!). Ants are tiny, so finding every entry might be impossible, but you can probably make it more difficult for them.
Ants (and most bugs) reeeaaaaally hate peppermint. If you can find where they're coming in, try spraying that area regularly with peppermint oil (watered down with water). Quick research also says they don't like cinnamon, so you could try that as well. Cloves and bay leaves are also apparently useful, but not with animals and babies who like to eat things.
If they're getting into your pantry or cabinets (or other places your children and pets can't get to), I'd recommend getting a couple of small traps to place in there. I think those are easily found at Home Depot and Lowes.
Wipe down any areas you see them crawling too. Ants leave a trail for their buddies that says "hey, this is a safe way to get food!" Honestly not sure what works best there, but I don't think you could ever go wrong with a good lysol wipe down your kitchen counter.
Good luck!