Mom's germ-repelling experiment wows millions in viral video

It's a science lesson, a health lesson and a super-viral video all in one.

On Facebook on Friday, mom of two Kelly Rose Sarno posted a video of her 4-year-old son, Declan, showing how soap repels germs in a simple experiment. It's since been shared 1.4 million times.

"My husband saw the trick posted on Barstool Sports and said he thought it would be a great experiment to show our 4-year-old when he got home from school," Sarno told "Good Morning America."

The Boston area mom of two said she thought her followers would enjoy the video, bur she never thought it would reach as far as it did.

"Everyone seems excited to share it with their littles," she said. "And there's lots of tags of teachers so they can try it in their classrooms."