Mulligan, who has autism, first became interested in garbage trucks after his mother, Robin Newberger, showed him videos of them to help him understand he didn't need to be afraid of their loud noises.
"He knows which trash can is going out on which day and notices them when we're driving and notices if they're out of line," Newberger told ABC News. "We will literally be waiting outside for hours on trash day because he hears the truck in the neighborhood and can't focus on anything else."
But this week when Daniel and his mom and dad, David, watched the usual pick-up, Manuel Sanchez, a recyclables collector not only picked up the trash but dropped off a special surprise for the young boy.
"He wants to give you something," Newberger says in the video. "Oh, Manuel, this is so sweet."
As seen in the video, Sanchez gave Daniel a toy garbage truck of his own, one that was identical to a Christmas present he'd accidentally broken.
"It was just amazing because it was the same one and Manuel had no idea," Newberger told ABC. She filmed the exchange between the two and posted it to Facebook.
Sanchez's act of kindness touched David's family and many others.
"This was something he did absolutely on his own," Nan Drake, spokesman of Sanchez's employer E.J. Harrison and Sons told ABC of the gift. "We're so proud of him."
Since the video has gone viral, Newberger created a special Facebook page called The Gift so parents can share uplifting stories about children struggling with autism.
"A lot of times, with kids with autism, it's just about the struggle," Newberger told ABC. "I'm glad it's showing the positive side of autism."