Allen, in her early thirties, ran an unlicensed daycare from a home in the Pioneer Park area of Kitchener from 2009 to 2011, according to police.
She appeared in court on Wednesday in a green sweat suit, with her head down.
Allen was accused of feeding the children tetrahydrozoline, a drug found in over-the-counter eye care products that can cause serious illness if ingested.
Court heard that one child who was given the noxious substance was a newborn at the time and is now showing developmental challenges.
Allen faces six years in prison, less time served.