We have a problem with ants in our hallway at the moment. We've put out traps, plugged in a sonar repeller and are squishing any we see.
Yesterday, DD (20 months) saw me stomp on one, said "Ant! Sad!" and burst into tears. She obviously doesn't understand death at that age, so I'm not sure what's provoked this reaction. I wondered if she was upset at the idea of ants in the house, but I asked her if she liked ants and she said yes, so it does seem to be my action that prompted her upset 
I thought she'd forget about it quickly, but every time she's been in the hallway since, she's said, "Ants!" and gotten tearful. I've apologised for stomping on the ant and told her that I'll move the others outside, where they'll live happily, but it doesn't seem to be consoling her. Any thoughts on how to handle this?