The proud parents posted the photos, which were an early Father's Day gift from Roxanne to her husband, to Facebook and they took off from there, provoking an "extreme" backlash, according to Finn's dad and Roxanne's husband, Mike Daly, 27.
"People threatened us," he tells PEOPLE. "Some said that our son should be taken from us. We're good parents and we would never have done anything to deliberately harm anybody."
What inspired such vitriol?
He honestly has no idea. His wife was just creating something "really cool," says Mike.
The photos pay homage to Batman, who's an icon in the Daly home.
"I love him because he's a normal guy, as far as superheroes go," says Mike, who's a retail marketing professional.
"He's got a lot of money but doesn't have any superpowers," he says. "And if you really know the character, you know he's completely psychotic but people look at him like this hero."
He's doing his best to instill his love for the superhero in his son as well.
Finn's bedroom wall is a Gotham mural and he sleeps in a Batman bed.
"He's starting to talk and 'Da-Da' and 'Ba-Man' are synonymous," says Mike.
He says that the Batman in the photos "might be me, but he's Batman, so I guess we can't know for sure."
Roxanne planned the shoot with the help of a local photographer, who met the family at the railroad location.
"We picked up Finn from daycare and drove out there after work, and it was a total surprise to me," he says. "The shoot happened really quickly and my head was kind of spinning the whole time. I never expected anything like that."
From Facebook, the photos migrated to content provider Unilad, and things spiraled down from there.
"Our photos got exposure for being unique, I guess, so it was perfect springboard for comments," he says.
Someone posted the family's address to a viral site and then said they were going to show up at their home at 3 a.m.
Beyond the menacing messages, "the biggest objection was that [being on railroad tracks] is dangerous or illegal," explains Mike.
"I mean, we had no idea it was illegal," he says. "I've never been on a railroad before. I'll never be on a railroad again. We don't hang out on them. I get where people are coming from, but I don't think the message was well-crafted at all. There were less aggressive ways of communicating that."
The Daly Family
Courtesy Daly family
Despite the negativity directed at the Daly family, Mike's takeaway from the Father's Day surprise is entirely positive.
"My wife did something extremely thoughtful and something that we'll remember for the rest of our lives," he says. "Her intention was to create something really cool and that's what I'm taking out of it.
"Some people are unhappy about everything and need to invent a reason for you to be unhappy about anything," he says. "So I try to ignore them."