It might be easier to talk with him if you don't call them warts, but instead refer to them as a virus. As in "I'm sorry, but since you have an active virus, I have to be really careful about exposure to me or my children". And then be vigilant about not using the bathroom at his house unless you have shoes and socks on. Make sure he keeps shoes and socks on at your house. Don't go swimming with him or to a gym.
The word plantar is the medical term for the bottom of the foot. Plantar warts can be single or they can occur in groups. They are caused by the HPV virus. They're not just unsightly - they are the active eruptions of a contagious virus. They are no laughing matter.
Plantar warts are not typically easy to transmit to others, except in warm moist environments, like swimming pools, hot tubs, showers, tubs, and the wet areas around those places like walkways, the pool deck, and bathroom floors that get a little wet from dripping towels or wet feet, etc.
If he has not been to a podiatrist and had this virus actively treated, that's a red flag. If he thinks they're nothing (like a freckle), he's very mistaken. If he thinks over-the-counter treatments are enough for 40 persistent viral outbreaks, he's wrong (the over-the-counter things can be helpful for one or two warts, when caught early). If he doesn't know that this is a virus that is contagious, he's misinformed. If he just assumes they're plantar warts and not another skin condition (if he diagnosed himself from a tv commercial or Dr. Google), that's a red flag. Make it a condition of dating him that he gets a real diagnosis and a real treatment from a real foot doctor.
I'm not a doctor, but my daughter had a persistent large plantar wart that didn't respond to treatment and the doctor was concerned enough that she had to cut it in a minor in-office surgical procedure. That solved the problem.