Rebecca Nelson took precautions to protect her severely food-allergic son at day care. He had a warning bracelet on his wrist, and supervisors were told about his condition.

But the bracelet wasn’t always visible, and the Alpharetta mother worried a harried caregiver might not see him eating something dangerous, or simply forget.

“You’re relying on someone who has their hands full,” she said. “I just didn’t feel comfortable. I thought there’s got to be something else I can do.”

So Nelson, a former baby gifts mall store owner, began making T-shirts that warned, in the gentlest way, that the preschool children wearing them could get terribly sick eating some very normal things. At first, she gave them to moms in similar need. Then, she launched Alert Clothing Co. The Johns Creek startup got going in earnest in 2008.

Nelson hopes to fill a business niche that has a number of competitors and stands to grow. Nearly 6 million children in the United States have food allergies, according to the Food Allergy and Anaphylaxis Network. Its CEO, Maria Acebal, called it “a growing and pressing public health concern.”

A 2008 study by the Centers for Disease Control and Prevention reported an 18 percent increase in food allergies from 1997 to 2007, and peanut allergies among children appeared to triple from 1997 to 2008. Every three minutes, a food allergy reaction sends someone to the emergency room.

Nelson called her customers “these really young kids who can’t advocate for themselves.”

Some doctors say such products can be helpful.

“There is a need for these kinds of products. We need these kinds of red flags,” said Dr. Neeta Ogden, an adult and pediatric allergist in New Jersey.

“If a child does have recurrent accidental exposures, then a product like this might help,” said Dr. Todd Rambasek, a Cleveland physician and American Academy of Allergy, Asthma and Immunology fellow.

For parents such as Amy Pott, it’s a clear but polite way to convey a crucial message. She bought Alert clothing for her dairy- and egg-allergic daughter.

“I wanted something that would tell people not to offer her a cookie, for example, without it being too serious or clinical-looking,” the Connecticut resident said. “Alert’s styles are so colorful and cute, while getting the point across effectively.”

Nelson won’t disclose sales figures but said her company is self-funded, low-revenue and not profitable. Getting word out has been hard, getting in stores harder. Business is seasonal: best in summer and at the start of school.

“I’m not making my living off this,” said Nelson, who is married with three children, now 15, 13 and 7. Two have serious food allergies. She sells via the company’s website (alertclothingcompany .com) and is trying to build awareness through outlets including doctors’ offices.

Nelson’s not a one-woman operation, but she’s close. She buys plain shirts, creates the designs, outsources the silk screening, warehouses the finished product and ships when orders are received.

The designs, also on tote bags, feature elephants, dinosaurs and butterflies, and they carry messages such as, “No nuts for me — thank you!”

“I want those kids to feel special,” Nelson said. “They are. They just can’t eat.”