I see field trips as still being in school, this includes getting to and from. So just as if another parent couldn't take little Timmy out of class and walk off with him. Parents can't make a pit stop with little Timmy in their car during a field trip to run a personal errand.
But this wasn't a personal errand. This was picking her kids up at school. And, if it's like my school, there is a limited time frame in which you can get the kids or you get in serious trouble with the school.
Sorry, but picking up other children (even if they are yours) from school is
a personal errand. It is definitely not part of the field trip.
If the field trip goes past the time you need to pick up other kids, don't volunteer as a driver.
If the field trip runs late and you really need to pick up your other kids, you need to tell some other adult from the preschool in advance, i.e., before everyone left the pumpkin patch.
I have some sympathy because I can see how the mom may have had a time frame in mind
3:00: Leave pumpkin patch
3:30 :Arrive Preschool and drop off kid
3:40 :Go to Elementary and pick up older kids
Then there is a delay leaving the pumpkin patch and she may not have noticed or may have noticed and thought she still had time to go to the preschool and then the older kids school.
Then she gets in the car and realises that there is no way she will be able to get to elementary school in time if she goes to the preschool first. So she tries to call and can't so fetches her children.
I mean I know that I often get in the car (with young children) and realise that it 10 or 15 minutes later than it should be because the time evaporates.
I wouldn't see it as a big deal if my kid arrived later in a convey.
Sorry, your bad time mangagement skills are your problem alone and should not impact other parents.
If everyone else has arrived and no one has been told where you went, other parents of your children are rightfully worried about their children.