And then, of course, there are the inevitable privacy concerns. Kinsa emphasizes that all data provided to the city will be aggregated and anonymized. “None of the individual data is going to anyone other than to that individual,” Mr. Singh said. “They own the data, and we’re really adamant about this.”

While digital privacy experts say that these are important safeguards, they also note that information about children and health is particularly sensitive. “It’s really important to balance the public health benefits and needs with the social or societal risks,” said Rachele Hendricks-Sturrup, the health policy counsel at the Future of Privacy Forum, a think tank focused on data privacy.

For instance, even de-identified data can sometimes be re-identified. “Even if it becomes ‘A fourth-grader at this school in this neighborhood,’ that could narrow it down,” said Hayley Tsukayama, a legislative activist at the Electronic Frontier Foundation, a digital privacy group. “It doesn’t take a lot of data points to re-identify something.”

The data, aggregated by ZIP code, will also be incorporated into illness signals that Kinsa makes available in its public HealthWeather map. The company sometimes shares this ZIP-code-level information with pharmacies, vaccine distributors and other companies. Clorox, for instance, has used Kinsa’s data to determine where to target its ads. (Lysol will have no special access to the data, Kinsa says.)

Both Kinsa and the city need to be transparent with families about how the data will be used, stored and shared and how long it will be retained, experts said. City officials are “essentially putting their stamp of approval on this,” said Amelia Vance, the director of youth and education privacy at the Future of Privacy Forum. “They need to make sure that they are living up to the trust that parents will have that this program has been fully vetted and is safe for their kids and their families.”

Over the coming months, city officials will keep close tabs on how well the program is working, Dr. Varma said. How do families feel about the program? Is there enough uptake to produce useful data? Can they actually catch outbreaks earlier — and slow the spread of disease?

“Our goal is to try to see whether or not, in the real world, whether it really does have that impact that we hope it does,” Dr. Varma said. “It’s also possible the system may not detect anything abnormal or unusual, but that it still proves to be successful because it provides people with information that they find useful and builds their confidence in having their kids at school.”