The mother of a five-year-old girl is pleading with parents to warn children never to touch needles after her daughter stumbled across a discarded one while at school.

Amy Slater took to Facebook with the warning Wednesday after her daughter, Lily and two of her kindergarten friends came across the needles and pricked themselves with them near St. Vincent De Paul Catholic School, an elementary school in Toronto's west end.

"It's usually a happy story post here on social media for us, but today, not so much," Slater said in the post, adding Lily had to undergo a blood transfusion to protect her from Hepatitis B and "intensive" HIV prophylaxis treatment as a result.

"We spent the day at the hospital with many tests and many tears," Slater said.

Toronto police said the incident happened Wednesday at around 11:30 a.m. at the school near Roncesvalles Avenue and Dundas Street West. Police say the children reached for the syringes, which were on the other side of a fence at the edge of school property.

A police spokesperson said it does not appear the children were injured, but that all three children, aged five, were treated at a hospital.

According to Toronto Public Health, the transmission of diseases through discarded needles is "extremely unlikely."

Globally, there are no recorded instances of HIV being transmitted by a discarded needle, and only five cases where a form of hepatitis was transmitted.

'We hope that it never happens again'

Slater told CBC News she got a phone call from the school's principal Wednesday, and immediately raced over. When she arrived, police and paramedics were already there.

Principal Laura DiManno escorted the parents and their children to the hospital, staying with them right into the evening.

"It's my school, they're my kids, they're a priority," she told CBC News. "It's an unfortunate event; we hope that it never happens again."

Slater says the hospital verified that none of the three children had drugs in their system, but will now have to begin taking 28 days of HIV antivirals.

Amy Slater took to Facebook with the warning Wednesday after her daughter, Lily, and two of her kindergarten friends came across the needles and poked themselves with them near St. Vincent De Paul Catholic School, an elementary school in Toronto's west end. (Mehrdad Nazarahari/CBC)

She said the school has a custodian who sweeps the perimeter of the property regularly, but that there would have been no way to spot the needles hidden in the grassy alleyway.

'No touching needles'

Police say the children reached for the syringes, which were on the other side of a fence at the edge of school property. (Shannon Martin/CBC) Parents have already been sent letters about the incident, DiManno said, and the school will also be holding an assembly, reminding students about what to do if they find dangerous items: never touch a syringe, and notify an adult immediately if they find any.

For her part, Lily is pleased she had a chance to ride in an ambulance, but she also says she learned an important lesson:

"No touching needles," she said.

Toronto residents can also call 311 to request help removing any syringes.