Then, just a few days later, the peanuts began to appear in the back yard.
"We removed all foods containing peanuts and tree nuts from our house to create a safer environment for our son. Imagine my dismay when I discovered peanuts in our back yard," Ellen Payne said.
At first she thought a handyman or construction worker had left the nuts, but after questioning workers she learned that no one had been snacking in the yard.
It didn't take long for the culprit to appear.
On Saturday morning, Payne spied a squirrel running on the fence clutching a nut shell, she said.
"A friend pointed out to me that many people enjoy feeding squirrels and leave nuts out for the animals to eat," she said.
The issue of stray peanuts and tree nuts is no trifling matter. Peanut allergy is the most common cause of food-related death, according to the Asthma and Allergy Foundation of America.
Three million people in the U.S. report being allergic to peanuts, tree nuts or both and less than 21 percent will ever outgrow the allergy, the American Academy of Allergy Asthma and Immunology reports.
Roughly one-third of persons with peanut allergies also are allergic to tree nuts, according to the Asthma and Allergy Foundation.
The likelihood that Oliver will encounter a peanut or tree nut as he plays in the back yard is increased as people put out bird and squirrel feeders, which often contain the nuts.
Squirrels "really do squirrel it away," according to Sandi Stadler, head of Palo Alto Animal Services.
The rodents just can't resist packing their cheeks full of the tasty fat- and protein-laden treats, and they can travel great distances to cache the food for the future or to feed their babies, she said.
Payne has yet to find the peanut source in her Midtown neighborhood. After Oliver's initial allergic reaction, she was tempted to post flyers around the neighborhood asking people to switch to less allergenic squirrel treats, but she decided to reach more residents by sending a plea through the Midtown Residents Association e-mail list, she said.
Given the population of peanut and allergy sufferers — 1 to 2 percent of Americans — she wonders how many other neighbors also are being exposed.
"Naturally the threat is worse with toddlers, who often put foreign objects into their mouths, but even some older children and adults have such severe food allergies that even being in close proximity to nuts can trigger an allergic reaction.
"I don't want to ask other people to stop feeding squirrels, which is something that so many others enjoy, but I would like to ask our Palo Alto neighbors to use safer alternatives, such as sunflower seeds, pumpkin seeds, squash seeds, corn or dried fruit — all of which are foods that squirrels enjoy but are not highly allergic to humans," she said.
Stadler said in all of her years of handling wildlife, the threat to human health by peanut- and nut-wielding squirrels is "absolutely new."
But she doesn't discount the threat to the health of squirrels — or any wildlife — that feeding them can cause. In short, Stadler doesn't recommend it.
"Feeding wildlife unnaturally brings a group (of animals) together," she said. When one animal gets sick, the illness quickly spreads, she added.
Palo Alto doesn't have an ordinance against feeding wildlife, although some cities do, including San Francisco, she said.
"How can you put a value on the pleasure some people receive from feeding wildlife? The squirrels are such clowns. But there are some real downsides to it," she said.