This is the moment two young siblings comforted each other after their quick thinking helped save their mother's life.

Mum Sarah James, 35, suffered a severe allergic reaction while home alone with her children, Lucas, 10, and Lucy, 8.

When Sarah collapsed, Lucas immediately called their family friend Mackenzie.

Mackenzie rushed to the house, phoned 911 on the way, and administered Sarah's EpiPen when she arrived.

Doorbell camera footage shows Lucas and Lucy hugging, terrified, as they wait for help.

Seconds later, Sarah's mum and a police officer sprint to the house - and almost immediately Sarah's dad rushes to comfort the children.

Sarah, a surgical tech from from Gillette, Wyoming, said: "It's been a really scary experience I think for everyone involved."

"I don't remember anything after telling Lucas to call Mackenzie, so it's all a bit of a blur."

"I know that without them calling for help, I would have certainly died."

"So, when I got my phone in the hospital and was able to check the notification on the doorbell camera, my heart just welled up."

Sarah had undergone knee surgery just 10 days earlier and was resting when the reaction hit.

She woke from a nap feeling flushed and itchy, so she took two Benadryl.

Minutes later, her lips and tongue began to swell.

She managed to call for Lucas before losing consciousness.

Lucas knew to call Mackenzie, who arrived in minutes and sent the children outside so she could administer the EpiPen.

In the meantime, Lucas called his grandparents, Sarah's mother and father, who live and work within a mile of the home.

The doorbell camera shows

Sarah's mother rushing to the door ahead of a cop and then her father arriving to comfort the children.

Sarah said: "It was such a mix of emotions watching the footage back."

"When I saw my mom arriving and running ahead of the cop it made me laugh."

"But then seeing my kids hold each other in that moment and then my dad coming up and just looking after them made me weep."

"I am so grateful to have family and friends that are able to be there in moments like these."

Sarah does not know what caused the allergic reaction, but she was treated with an Epi drip and IV steroids.

At the hospital, she was intubated, given a chest x-ray and CT scan, which revealed that she also had a pulmonary embolism in each lung.

Doctors told Sarah that if either of these blood clots had continued to grow, she could have easily died.

Sarah said: "All of it was pretty terrifying."

"If my kids hadn't called for help when they did, I would not only be dead from an allergic reaction, but also have no idea that I had these ticking time bombs in my chest."

"We still don't know what caused the allergic reaction, but I have sent a bunch of allergy tests off to find out."

"I was in hospital for about four days being treated with IV steroids until I was ready to switch to oral medication."

"I'm on blood thinners for the next few months for the emboli in my lungs and am also weening myself off the steroid pills."