My two year old nephew has been complaining about tooth pain the past 2 days. we recently switched to a fluoride-free toothpaste, could this be causing it?

Tooth pain: Fluoride-free and fluoride toothpaste do not cause tooth pain in toddlers. More likely new teeth are coming in and causing the discomfort.

Doubtful: Fluoride (or lack of it) does not cause tooth pain. He might be teething. Which tooth? Was it traumatized? When he is old enough to spit out and not swallow the toothpaste, consider one with fluoride... he and his teeth will thank you for it in the years to come. If the pain continues, have him see a local pediatric dentist.