@Sean There may have been some use in dealing with resistant Victorian children but most likely what drove the Nannies and Nurses use of glycerin was insuring those venturing out of the home were prepared for the outing when given short notice.
Public restrooms during the Victorian years and beyond left a lot to be desired in cleanliness. So the matriarch in a family did not want to stop while venturing out, for use of public facilities that frequently had liquids on the floor and toilets that might have been cleaned once a year. The proper Victorian woman's dress would easily be soiled in such facilities while caring for a child. Add into the equation, if visiting a friend, it was considered poor form to use your host's toileting facility, the chamberpot. In addition to the house staff carrying out the chamberpot immediately after use, most housekeeping staff would fire up the lavender burner to overwhelm any odors unleashed during the visit. It was embarrassing for both the guest and the host. The other wart in the lifestyle for women was the layered clothing. Many were corseted, making removal of undergarments time consuming and tedious. In order to use the chamberpot, women usually had to substantially disrobe, as the outer dress with the hoop skirt/panier/bustle made setting on the pot dangerous if not removed.
Proper Victorian women were well acquainted with the fine art of clearing the colon to open a time window where they could venture out for upwards of eight to twelve hours, leaving only voiding as an issue. They carefully chose foods that did not disrupt the bowel, did not produce flatulence to a troublesome degree and did not produce patently offensive pungent odors. If the matriarch was taking children along, the nanny or other carer was alerted so that plans could be made to insure the children's colon's were similarly cleared.
If taking the children was an impromptu decision, and time was short then glycerin often was the Nanny's weapon of choice. Preparation took a minute, results occurred in minutes, and an uncooperative retentive child was literally forced to poop.
Another thing during the Victorian era was use of pure glycerin. 50% Water-50% glycerin in more than sufficient to induce movement and creates less discomfort. 1 - 2 milliLitres of glycerin will move the most resistant gut in five to ten minutes. The imported Asian figs are pure glycerin and provide a delivered dose of about 10 to 25 milliLitres glycerin. Movement with 25 milliLitres will occur within two minutes, often involuntarily. If it takes longer then there is normally some neurological disorder that dulls the stimulus.