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Speaking from personal experience, it really depends on the daycare. Some daycares (in Canada) will call parents if you don't show up by a certain time and some daycares don't.
It depends on the family as well. When you have a family that drops off their kid whenever, with no consistency, because maybe their work schedule is all over the place, or maybe they have access to other caregivers, then it isn't too unusual when there are days you don't show up.
There are also families who are very close to other families at the daycare. Teachers know they see each other outside of school. One day a mom might walk in and mention that their friend's kid is sick and won't be coming in to daycare that day, and no further questions would be asked.