Anyone know what this could possibly be from?

This wart has popped up on my sons finger about 2 weeks ago and has grown in size he hasn’t be around any frogs that I’m aware. Just want to add that my son currently lives with his dad as it’s the best option right now so I’m not around him all the time but I do visit him regularly and I’m a bit worried. He says it doesn’t hurt he’s 3 years old I’ve voiced my concerns to his dad but he seems to not be worried at all.