To her 3-year-old sister, Bailey, the discs looked like pennies.
Penny? Their dad thought. What penny?
Brock Thompson looked at Shelby and saw she was breathing fine. He scanned the table. Most of the batteries were still in the package. Most, not all.
One was on the floor - with teeth marks in it.
Shelby spit up. Instead of the familiar odor of sour milk, Thompson smelled the acrid stench of metal.
"I freaked out. I thought maybe it was melting her insides," Thompson recalled.
He called his wife, Sarah Thompson, who was running errands. They called their pediatrician. Waiting for his return call, they jumped online to read. Shelby threw up more. The Raymore, Mo., family raced to a Kansas City emergency room. After taking an X-ray, physicians sent them on an ambulance ride to Children's Mercy Hospital.
"Next thing we knew, Shelby was in the hospital..." said Sarah Thompson. "It was so scary."
The battery had lodged in Shelby's esophagus. Endoscopic surgery removed it. Still, in four hours, one entire side of the disc battery had burned away, exposing its black surface.
Shelby is fine, now, said Brock Thompson. But she'll be hearing about this baby story for years to come.
"You know, it's one thing to take away something dangerous that you see them playing with. But I had no idea that something high up on the kitchen table was such a threat. I felt terrible."
Nationwide, button batteries are ingested by some 3,000 people a year, according to the National Button Battery Ingestion Hotline in Washington, D.C.
Gary Wasserman, a pediatric medical toxicologist at Children's Mercy Hospitals and Clinics, has treated a lot of the patients who stuck crayons in their noses, swallowed parts of a toy or ingested a button battery.
"Although 90 percent of those ingested batteries pass through without any harm, all of the incidents require a trip to the emergency room to get an X-ray to make sure it didn't get hung up in the esophagus or food canal," he said.
Through a child's eyes, so many things look like something good to go in their mouths, he said.
"Mothballs could be marshmallows. Pine oil cleaners could be apple juice. Powder cleaners could be parmesan cheese.... Pennies get stuck in throats. And those toys with magnets can cause some real problems."
Wasserman has even treated babies who tried drinking baby powder, thinking it's white like a bottle of milk, and then aspirated the fine dust into their lungs while the parent was busy changing their diaper.
"You have to stay ahead of the child's development to really try and see things the way they do," he said.
The button batteries are in more products year after year, found in a variety of objects from watches and clocks, cameras, key chains, remotes, greeting cards, shoes and lighted jewelry.
But nearly half of ingested batteries are from hearing aids, according to the battery hot line. Adults and older children ingest these batteries too, using their mouths as a "third hand" when replacing the tiny disc-like wafers.
But grown-ups know to seek help. Babies might not have the words to tell them.
"Parents can forget that their child is developing enough to pull open a drawer, climb on a counter, even get into a visitor's purse and eat their medicines," Wasserman said.
Child-proofing your house can be as easy as crawling around, he said.
"Get down on all fours and look around. Think like a child and you'll see the dangers."